Hi Jon,
I can only tell you my experience with Luna and it varies clutch to clutch (never bred). Last December (2003) she began showing rec. colors and I figured she would lay in a bout a month - she laid in May!! Do I know why? Not a clue! Her July clutch and her December (2004) clutch were each about 4-6 weeks before actually laying.
Be sure to not feed her a whole lot and to make sure she gets enough calcium (just don't overdue it). If she is like Luna, and stops eating completely, you may want to talk to your vet about liquid calcium. If she is more like normal chams who will eat during most of it your regular routine is probably OK maybe add the calcium dust one more time a week - keep your gutload healthy and if you can, feed her small silkies for added calcium.
I think waiting thru one fertile clutch is probably a good idea, if for no other reason than for you to know what to expect when you have little ones on the line! This time will be like a dry run! 
just my 2 cents - good luck!
lele
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0.1 veiled - Luna
0.2 felines - Kyndra and Líta
1.0 African Clawed Frog - Skipper
0.5 Mad. Hissers
0.1 Chilean Rose Hair Tarantula (no name yet)
?.? Goliath Bird-Eater Tarantula (no name yet)