IMO, putting clowns and an anemone inside a "critter cage" is a very bad idea. Forcing a clown to be hosted before it is ready could very well end up with a injured clown, or even a dead one.
A week really isn't all that long to wait. Can take minutes, hours, days, weeks, months, etc. Also, I have yet to hear any proof that TR clowns have had their inborn instinct to be hosted breed out of them. IME, all of my TR clowns have been hosted.