I think whenever someone can reply, though like Smy[@Smystar99] said -  don't leave anyone behind without at least a single post in a scene.

That is, unless they haven't posted for like 3-4 days and everyone else has already posted. 

[@auspiciousPetal]Would your introduction also include why they were there in the first place?[i] Sleepover? Group project? Midnight pr0n watching?[/i] If not, we could totally start making up reasons ourselves. But if you already have something in mind, I'm alright with that too.