8.30 till 10 mite be abit to long ino most people have there lights on a 12hour cycle. i have mine 8 till 8 and he will go and hide/settle in for the nite about 7.30 he's probably geting settled for the nite and waiting for you to turn the lights off.
you got lucky he didnt go for a wonder, id make sure you have everything you need outside before you take you cham out so you dont need to go back inside for anything
how olds your cham? they start show there colours around 6month old and will take up to a year old to come out in all its colours mines abwt a year and half old you can have alook if you like in my album on my profile:)