Sativas 10 wks flowering IDK when they'll be ready to start flushing

The seeds I used for this grow were cross bred. The father mostly sativa, ww & ice and mother, good home grown. I got the seeds thru nirvana. The only info their web site gives on the 'White castle' is that the flowering period is 'medium'. So I have no idea how many weeks before flushing & harvest. With such info as they gave, can anyone guess at how many weeks. I'm guessing 16 weeks? They are beautiful and filling out greatly. I've just now had to tie them up to brace them the branches were starting to hang down. The buds are still putting on weight and still new growth. No signs of amber color anywhere. Sorry i can't do pic's. This is the best grow so far. I've not done sativas before. What will be first signs that they will be ready for flushing?

a 100% pure sativa can take up to 16 weeks, but not usually, pics would be very helpful.

I would say once you see the trich's getting milky then flush. because then they will start turning amber, which signals harvest if im correct. just check around Im sure there is a tried method people grow bagseed all the time. no instructions there, so Im sure there some way to know.

Like don't the white hairs start to turn amber too when it's getting close? I read somewhere that sativas could take up to 26 weeks. Would that have been total time from veg to finish? Or 26 weeks flowering time? You said 100% sativas take up to 16 weeks.