They breed when they're ready and there's little you can do about it. You realize, of course, that jax need to be in separate, visually isolated cages? To see if they're ready for breeding you introduce the female into the male's cage or introduce them on neutral ground (such as a large Ficus plant). If the female turns dark and starts rocking, she's not ready. Separate them and try again ina day or two. WQhen she's ready she'll remain green & allow the male to approach.
There are many good web sites for jax info. See www.adcham.com in the txonomy section and see http://www.geocities.com/chamjacksonii/.
and
http://chamownersweb.tripod.com/
Ed