I know when I got Mavis and Beulah, Mavis wasn't too sure about the new "people rat" in her life, Beulah thought it was great, but I just threw on a couch cover and we all hung out on the couch for an hour or more each night (and some time during the days). Exploring,chittering and being held for a few minutes at a time. After a day or so it was a routine they looked forward to for the next year and a half.
When Beulah died a few months back, I got Louise and Basil so that Mavis wouldn't be so lonely. And did the same thing,(by then I learned to have several rotating couch covers for rat time).
Since Basil proved to be pregnant (geeze) There are now 6 girls having couch time every night and after they have tired there are 6 boys having couch time.
Once a rat is settled in with you they will look forward to coming out and spending time with you, so much they will raise cain when it is time to go in and try to guilt you out everytime you are in range of the cage. Nothing looks more pityful than a rat holding onto the cage peering out at you and looking like they never, never get out to play....ever!
Mine have Day Condo's, (sunshine and fresh air on the porch) and then they have their night sleeping cages inside.