How long does it take to replace a timing belt on a 99 Toyota solara?

Time required for that job depends on tools available (air vs manual) and experience. Someone who's done it before might take a couple of hours start to finish. Those that haven't could spend an entire day on it.

I'd suggest you download a factory service manual from Toyota or pick up a Clymer's manual (auto supply or online). Both will provide detailed procedures and valuable pictures.

Cheers