Hi, Coldgravy...
Welcome to AFN.
Your question can't really be answered without pictures and/or more information.
A couple things are used to gauge the maturity/harvestability of a plant.
The first is the condition and color of the trichomes (The little "crystals" on the small sugar leaves and flowers)
They start with clear heads, mature into having cloudy (translucent, milky white) heads and then finally mature into amber heads
Some never amber up, most do...all three conditions will be present at a single time
and as a result people refer to these in percentages...i.e. mostly cloudy with 30% amber.
What you want on those percentages is reliant on what kind of high you want and what strain you are growing.
The other metric used to gauge maturity is the condition and color of the fan leaves (the larger leaves that store nutrients in them)
As the plant reaches completion, it will start to feed on and drain the fan leaves of these stored nutrients
so they will yellow and start to die (at the tips first, and work it's way inward)
That's why we need pics or details about those items
It is relatively safe to guess that you are "in the window of opportunity" at 75 days, though...
Just so strain and condition reliant that it's impossible to say.