Best Time to Harvest for the Most Weight

These are the strains im growing with their flowering times next to them: Critical Yumboldt(7-8weeks), Fast Nevilles(8-9weeks), The church(9weeks), WW X BB(7-8weeks), Sugar Black Rose(7-8weeks). My question is, i'm thinking of just harvesting all my plants at 9 weeks since one of my strains ends at that time and i want to pack on as much weight as i can on all my girls. Is that a good idea or does that sound like i would be over-harvesting some of my stash? Anyone have any input on this matter? IF so + REPS.
P.S. I don't have the money to invest in a microscrope to check when to harvest.

The weeks listed are not exact....they are guide lines. Watch your plants and watch your trichomes and you will see when they are ready, some take 8wks and some might take 11wks. Taking them all at the same time will result in some being peak ripeness and some being underdone. Even amongst siblings of the same strain there can be a lot of variation from one plant to the next so tackle it with that perspective...or don't...

Just look at your plant, if the buds look swelled and the hairs have receded then you're probably looking at the best time to harvest them, weight wise.