Carefully repot into well-draining son. Eventually it will need a larger pot - or plant it in the ground in suitable areas.
If the temperature regularly gets over about 85-90 degrees in the summer, it's a good idea to give it some afternoon shade. If the leaves ever wilt too much, simply give it some more shade. Keep in mind that Cherimoya has naturally droopy-looking leaves.
Dormancy care -- They don't exactly go dormant - they shed their leaves in the spring (April/May here in Calif), and new leaves appear a month later. Seedlings sometimes don't shed their leaves the first couple winters. If your plant doesn't shed its leaves by the end of May, i would manually defoliate them. To do this, simply snap back a leaf at its base and remove it. A new leaf will appear from the same spot - in fact, you might see a little green "nub" of the next leaf underneath.
When they approach flowering size, try to give them around 50-100 hours at below 45-48° F (9°C).
For more info on growing Cherimoya, see : http://www.crfg.org/pubs/ff/cherimoya.html
There is also a great website on Cherimoyas here: http://cherimoya.orcon.net.nz/
If you have any questions, feel free to email me.
Strange Wonderful Things