how do u know how many days or weeks ur plants in flowering?..when do i start..like when is the first sign to know. thanks

are these indoors or out ..lol..you will see the female pistols start to gather into buds ..most strains are around 7 to 10 weeks with the majority of the indica strains being around 8 weeks ..sativia will in general run about 9 weeks ....
once they are about as big as they get the buds will start to have trichroms on them and thats what produces the thc that your after ..you will need a magnifying glass to see these clearly and they will turn from a clear looking to a milky then to an amber ..when they are about 20 to 40 % amber they are done ..some like a smaller amount of amber and others prefer a larger amount amber ..its your call on that ..also most plants will outdoors will start to move from a vegg state to a budding state when the days start to become shorter as fall starts to move in ..if indoors when you flip to 12/12 on the timer for your lites ..haha ..hope this helps ..