I always thought it takes about 30 min ~ 1 hour, may be 2 hours but no more... For example, Tom go outside at night quite often, but he mustn't come back too many hours later, because his parents wouldn't like it ^_^' So I imagined it wasn't too long... But it's true we don't have any good explanation about that. No really more about how they give back the good host to his Yeerk. But I imagined somebody say with ultrasounds (as they speak in the pool) who should come back for each host... (I tried to imagine in my fanfiction ^_^' but of course you can't read, it's in French)
Tom could just go to a Sharing meeting, and go to the Yeerk pool during that meeting.
Hork-Bajir Chronicles: I read of Yeerks (such as the future Viisser 3) being summoned to infest a host.
