Quote from Plaguescarred >>

Quote from Brad_Paradox >>

So.... did I just cause the creature to flee and otherwise lose its turn both during its current turn AND during its "next turn"? 

 Yes it would because Command duration is Instantaneous it's not subject to Combining Spell Effects limitation for example.

 I'm not sure how that allows them to affect two different Turns.

Quote from Deyric >>

3 Sage Advice entries:

"Casting Time Is there a limit on the number of spells you can cast on your turn?

There’s no rule that states you can cast only X number of spells on your turn, but there are some practical limitations. The main limiting factor is your action. Many spells require an action to cast, and unless a feature says otherwise, you only have one action on your turn. You also must abide by the rule of only expending one spell slot to cast a spell on your turn.

So, for example, if you take your Bonus Action to cast Healing Word using a spell slot, you can also take the Magic action to cast Vicious Mockery—a cantrip which doesn’t require a spell slot."
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"Can you cast a Reaction spell on your turn?

Yes, but you must abide by the rule of expending only one spell slot to cast a spell on your turn. For example, if you take a Magic action to cast Fireball using a spell slot and an enemy casts Counterspell, you can’t also then expend a spell slot to cast Counterspell targeting that enemy."
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"Can you use a melee spell attack to make an Opportunity Attack?

No, you can’t cast a spell when a creature provokes an Opportunity Attack from you. This is because each spell has a casting time. For example, the Chill Touch spell has a casting time of an action. A game mechanic, such as Opportunity Attack, doesn’t let you alter that casting time unless a feature says otherwise (see the War Caster feat for an example of this)."

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The first two explicitly enforce the casting limit per turn rule.  But do say "On your Turn."

The last Sage entry I posted seems to imply Warcaster is an exception and grants the ability to supersede the casting limit. Specifically mentioning the feat as an exception to the previous posts.   And this is not 'on your turn' either. 

If opportunity attacks let you exceed your melee attack limit without any feat at all, why wouldn't Warcaster, when you have to delve into a feat to even do so. 

I can't find anything else official. 

 Warcaster doesn't affect how many spells you can cast on your Turn. What it does do is allow spells that require an Action to cast to be fast as a Reaction - contrary to the normal rules. That's what it's talking about. If you cast a Reaction spell on your Turn, then it counts towards the maximum of one levelled spell per Turn. However, War Caster is being invoked on a different person's Turn so it doesn't matter anyway. The spell limit refreshes on a new Turn, rather than Round, so it's fine.

The question asked though is whether Command cast by War Caster affects the creature both the current Turn and the following one, which is different.

Quote from Linklite >>

Quote from Plaguescarred >>

Quote from Brad_Paradox >>

So.... did I just cause the creature to flee and otherwise lose its turn both during its current turn AND during its "next turn"? 

 Yes it would because Command duration is Instantaneous it's not subject to Combining Spell Effects limitation for example.

 I'm not sure how that allows them to affect two different Turns.

Because they ''follow the command on its next turn'' effectively meaning; 

1. The effect of previous Command occuring on the target's turn.

AND

2. The effect of current Command occuring on the target's next turn.