well put G! For the most part, anything past 24 hrs wont kill you. But do make sure you keep it clean. Although if youre sanding you'll have to bathe it anyway which means it wont matter much if it gets dirty. I dont sand inbetween paint coats, but I do in between prime and paint.
Heres my process for you all.
In a dark stock color, i prime white. Then soon as she's dried, 800 wet sand and paint coat 1. After 15 minutes (duplicolor you can handle in 20ish) I slap coat 2 on. Let that one dry for 30 minutes. then 1000 dry sand, CO2 blow off, and 3rd coat. Clear coat when ready for it.
Thats the method, and it's produced some seriously even smooth paintjobs.