It will reset after X amount of engine start cycles. When that happened
to me last Summer it took about 3 days. Annoying, but not really a problem.

Gary

Normally, it should reset itself after a couple of rides where the computer
will ascertain that the fault is really fixed. Otherwise you need an OBDII
reader to erase it if you want it out sooner.  That being said, if the fault
did not really disappear, i.e., you think it is the gas cap but it is in
fact something else, the light will stay on. I have a 2000 Camry with a
check engine light which turned on after I refuelled. I suspected the gas
cap but, in fact, it was my VSV (vacuum switching valve) for EVAP which
required replacement. The light extinguished shortly after its replacement.
Hope that answers your question.
JG

At least on a 95 - removing the EFI fuse for 30 seconds with the
ignition switch to off will clear the trouble code.  Alternatively,
you can remove the battery (for 30 seconds with ignition off?).

To ascertain that it was really the gas cap you would need to first
read the code.  Are you sure thats the problem?

Autozone will read your code for free.  The camry chilton repair
manual at your local book store will explain the procedure for your
specific year.