So you only get the 10 temporary hitpoints after an hour has passed?

The effects of the potion last for one hour after drinking it, I believe, though there seems to be a confusing redundancy to the wording.

It says, "For 1 hour after drinking it, you gain 10 temporary hit points that last for 1 hour."
They way you interpreted it, the wording would have to change to:
"In 1 hour, after you drink it, you gain 10 temporary hit points that last for 1 hour." 

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So the actual effect is on round 1 you drink it and gain 10 temp hp.  Those hp last for 1 hour. So if you had 50 hp, and drank the potion you'd have 50+(10) hp. Or 60 total hp.  If you take 6 hp of damage you'd have 50+(4) hp.  If the hour were to pass you'd then have 50 hp loosing the left over extra 4.  You DO NOT loose a full 10 hp after the hour ends. If you were below 50 hp when the hour ended you'd loose no additional hp.

How much would this item cost if it were sold by a rare potions dealer?

Rare costs anywhere between 501-5000gp

It seems to me like the redundant wording is possibly because an earlier draft of this gave you the temp HP every round for the hour as thats what the spell does but then they decided to remove that effect but didn't do a great job of redrafting the text.

"For 1 hour after drinking it, you gain 10 temporary hit points [at the start of every turn] that last for 1 hour"

To be honest if i gave my party this potion i think I'd add that back in but knock the HP down to 5 like the spell version, seems a bit of a damp squib otherwise.

no the way i see it is, you drink it.... you get 10 temp HP that last for an hour. that's it. once the temp hp is gone it's done no more temp hp. it doesn't increase your max hp.

no extra 10 temp hp every round...no waiting an hour until the effects you. that's it.

Potion of Heroism: Gives the bless spell

I'd word it as:

You are under the effects of the bless spell for an hour (no concentration required).
You gain 10 temporary hit points, it expires after 1 hour has passed.

So do you regain 10 temp HP per round for the hour that the potion is active or is this just a flat 10 hp that doesn't regenerate if it gets expended?

You only get 10 then when its gone, its gone

Why is no one talking about how amazing 1 hour bless with no concentration is?

Because 1 hour of heroism with no concentration is even better?

Potion of Bless. Thanks.

This effect doesn't stack with a cast Bless spell, right?

lasts an hour from the moment you drink it