I never mate a female veiled until she is at least a year old.
To mate them I hold the female outside the male's cage so they can see each other. I watch for the reactions.
If the male inflates his body, takes on his bright colors, head bobs to her but DOES NOT hold his front foot up, hiss or gape then he is recognizing her as a female that is receptive.
If she hisses, gapes, sways back and forth and darkens the background color to almost black, etc. then she is non-receptive....and should NOT be put in with the male.
If the female remains calm, keeps her usual green colors, move slowly away from the male she is receptive...and can be put in with the male....but watch them for a bit to see that things remain good.
Once they are getting along okay, they can be left together until the female starts to reject the male by darkening her background colors to almost black, hissing, gaping, swaying back and forth, lunging at the male, etc....at which time she should be put back into her own cage.