the calcuations for achievements reducing gem time are not accurate
i have 53 which is 53%
ye it takes 39 minutes to get a gem
no, the calculation you said is wrong.
the true calculation is increase the accumulation speed not decreasing upper limit of the time needed
example:
if you get 1 p/min, the gauge need 60p, then you need 60 min to complete once.
generation speed is multiple to the 1p/min.
with mean, you accumulate 1.53p/min, then you need around 39min 24sec to complete once