There is no definite time for a female to lay her first clutch. It depends to some extent on the husbandry and her rate of growth. What I can tell you is that a female veiled will get mustardy/yellowish splotches indicating that she is becoming mature and then bright blue dots indicating that she is receptive. If she shows a dark background color she is non-receptive/gravid....although she can drop this color during the time she's non-receptiv/gravid at times too.
Its also not definite about the time between clutches. It depends partly on when during the cycle she is mated to some extent.
Regarding the container for her to dig in....I put an opaque container (of washed playsand) a minimum size of 12" deep x 12" x 8" in the cage so she will have a place to dig to show you she needs to lay. Some females will actually lay the eggs in these containers...but they can also be moved to a larger container once they start to dig. I don't usually worry about keeping the sand moist until the female starts digging or I know she is close.
When the female is digging, its important not to let her see you watching her.
Here's how the digging/laying should go....
she may dig a few test holes but should finally chose one and dig it until she is satisfied with it. She should then turn around bum down and lay the eggs (often in the evening), fill the hole in and tamp it down....and return to the branches.
