Dry to the touch is acceptable for the second coat. If you're repainting one room, paint the trim and door, cut in the walls and roll. Apply the second coat to trim and door and by the time you're done with trim, it's safe to recoat the walls.

Air movement also helps, as long as you're not moving dust through the room.

Once I was in a rush and did a second coat very soon after the first, the next morning I had a crackle finish!

I always wondered why exactly that happened? I can only guess not enough dry time between coats.

Luckily, it was very subtle and you had to get right up to the wall to see it, so I lived with it for 10 years! Till I finally repainted in order to sell the house. Repainting looked fine, covered the crackle without a trace.