If BC obtains a TPE in a trade for Bosh, he will have up to a year to use it. The Raps would be getting the type of exception that applies to non-simultaneous trades.
The CBA is a bit convoluted in places, but Larry Coon has created a useful FAQ page. Moremilk, MangoKid, and the other guys who accurately discuss cap issues tend to consult this site for their information:
NBA Salary Cap FAQ