If you popped it from seed, newly germinated seeds need about 6 weeks veg before they show presex signs. Once that mother plant is 6 weeks then any clones taken will be ready to go as soon as they root. As advised a few times above, make absolutely sure the dark time is 100% dark. its been stated so many times because its that important. Patience padawan and you will be rewarded. Also a crumb to keep you perky: in my 23 yrs around plants the males have always showed before the females. If it takes a long time id bet its a baby girl.
If you really are that worried i am currently breeding Blue Widow and i would be more than happy to show you some pics of male flowers...actually i think there is one in my journal.
Happy growing.
-ST