I recently adopted a second guinea pig, Rosie, to introduce to my guinea pig Penny. The introduction is happening right now. Penny was the only one showing any dominance behaviors, and she stopped about an hour in. However, Rosie makes distressed sounds whenever Penny approaches her to sniff her butt or chin. The piggies have now been in the same playpen for about five and a half hours, with no signs of aggression from either side after the first hour. How will I know when it's okay to move them to the cage (which I have already cleaned)? Should I wait until Rosie feels more comfortable with Penny around, or will that take time? If they're not ready to move into a cage together when all the humans in the house have to go to bed, is it safe to leave them in the playpen (with food and water, of course) overnight?