If you use Nystul's Magical Aura to make this spell think a zombie is a beast, does it remain INT 10 after Nystul's wears off in 24 hours?

Quote from BenTenBlessing >>

If you use Nystul's Magical Aura to make this spell think a zombie is a beast, does it remain INT 10 after Nystul's wears off in 24 hours?

 I don't know but it's a very good question

I can't think of much in the official rules about creatures changing their creature type, but I would personally rule a creature is no longer affected by an effect that doesn't work on its new creature type.
Awaken being an Instantaneous effect means that probably doesn't apply, though
An awakened animal isn't under the effect of Awaken, otherwise the duration would be Until Dispelled

I don't think they considered that particular combination of spells carefully enough...

what would happen if a beast with 4 or more INT was under an effect that reduced its INT to 3 or under, than you casted awaken, and then the INT-reducing effect wore off

Quote from LizardfolkWarrior >>

what would happen if a beast with 4 or more INT was under an effect that reduced its INT to 3 or under, than you casted awaken, and then the INT-reducing effect wore off

I'd be inclined to say that since this spell has an instantaneous duration and its Intelligence-enhancing effect is intended to be permanent, the other effect ending doesn't change anything. That is, the target would keep its new Intelligence score of 10. 

It would be different, maybe, if this were an ongoing spell that ended after a certain number of hours or something?

How does casting this spell actually work?

Do I have to select the target before I start casting, or can I do so when I finish?

Do I have to touch the target immediately after I finish casting or can there be a delay? 

The general spell-casting rules (surprisingly) don't actually say that you have to select a target before starting casting a spell. For most spells that wouldn't be relevant, but it would be for long-casting-time touch spells.  Most of _those_ don't actually describe how or when you touch the target.  The main exceptions I can find are this, and Simulacrum. 

Simulacrum (2024 version) specifically states that you have to remain within 10ft of the target and the simulacrum for the duration of casting, and have to touch them to complete the spell.  Awaken _doesn't_ make such a restriction, so one could plausibly interprete it to mean you can spend your 8 hours casting the spell, and then at any time after that touch any creature to awaken it. Which could allow all sorts of fun shenanigans, but feels like it's not intended rules-as-intended.

I am a novice player, but it seems reasonable to interpret "and then" as a sort of Ready action or delayed trigger to defer your target selection, although Ready does specifically state that it is only applicable to spells with a casting time of an action.
"You spend [8 hours] tracing magical pathways within a precious gemstone, and then [for an instantaneous duration] touch the target."

I'm curious as to the utility of this spell?  At 5th level a CR 0 (shrub) or CR 2 (tree) don't seem particularly significant, but I'm probably missing something.  Also, I'm trying to imagine when the 8-hour casting time would allow for this spell to feasible, since you can't cast this while also doing a long rest, and not sure how often the rest of the party is going to be willing to wait for you to cast a spell like this that doesn't seem to be of any major benefit to the party (again, I'm probably  missing something here).

Quote from sethtucker1 >>

I'm curious as to the utility of this spell?  At 5th level a CR 0 (shrub) or CR 2 (tree) don't seem particularly significant, but I'm probably missing something.  Also, I'm trying to imagine when the 8-hour casting time would allow for this spell to feasible, since you can't cast this while also doing a long rest, and not sure how often the rest of the party is going to be willing to wait for you to cast a spell like this that doesn't seem to be of any major benefit to the party (again, I'm probably  missing something here).

The spell is pretty niche. There are a bunch of higher-level spells that seem like they're intended more as plot points than as spells you throw around all the time. 

That said, it sounds like you may be missing the fact that you don't have to use it on a plant; you can also use it on any creature with the Beast or Plant creature type as long as its Intelligence is 3 or less. 

This spell is more commonly used on beasts with low intelligence. Consider a Plesiosaurus that now has an INT of 10, which happens in a popular module. You're essentially giving sentience to beasts. You could create your home surrounded by sentient intelligent beasts that have been awoken and can speak Common, or whatever language you choose.

Quote from Iapetus303 >>

How does casting this spell actually work?

Do I have to select the target before I start casting, or can I do so when I finish?

Do I have to touch the target immediately after I finish casting or can there be a delay? 

 

The general spell-casting rules (surprisingly) don't actually say that you have to select a target before starting casting a spell. For most spells that wouldn't be relevant, but it would be for long-casting-time touch spells.  Most of _those_ don't actually describe how or when you touch the target.  The main exceptions I can find are this, and Simulacrum. 

Simulacrum (2024 version) specifically states that you have to remain within 10ft of the target and the simulacrum for the duration of casting, and have to touch them to complete the spell.  Awaken _doesn't_ make such a restriction, so one could plausibly interprete it to mean you can spend your 8 hours casting the spell, and then at any time after that touch any creature to awaken it. Which could allow all sorts of fun shenanigans, but feels like it's not intended rules-as-intended.

 This is a grey area in the rules. Personally I would say that this spell doesn’t say that you have to declare your target when you start casting it, you effectively choose your target when the spell takes effect. Honestly I think all the “fun shenanigans” you could easily think of with this spell is rules as intended, or at the very least someone at Wizards probably knew players would do weird and interesting things with the target selection and decided to allow it.

As for when you have to touch the target, the rules as written say that a spell takes effect immediately after you finish casting it, but for a spell like this most DMs will probably let you delay it so long as you continue using the Magic action every turn.

Quote from wagnarokkr >>

Quote from sethtucker1 >>

I'm curious as to the utility of this spell?  At 5th level a CR 0 (shrub) or CR 2 (tree) don't seem particularly significant, but I'm probably missing something.  Also, I'm trying to imagine when the 8-hour casting time would allow for this spell to feasible, since you can't cast this while also doing a long rest, and not sure how often the rest of the party is going to be willing to wait for you to cast a spell like this that doesn't seem to be of any major benefit to the party (again, I'm probably  missing something here).

The spell is pretty niche. There are a bunch of higher-level spells that seem like they're intended more as plot points than as spells you throw around all the time. 

That said, it sounds like you may be missing the fact that you don't have to use it on a plant; you can also use it on any creature with the Beast or Plant creature type as long as its Intelligence is 3 or less. 

 I would probably use it to defend my home base rather than use awakened creatures in combat, unless I come across a particularly powerful or useful creature to cast it on. One of the big benefits of this spell is there’s no limit to the number of creatures you can awaken so long as you have enough resources.