let's do math to see how long we play with out gears
gem1............8 hours
gem2............24 hours
gem3.............48hours
Suppose the chance of super gem is 10%( i would say lower than this)
replacing 1 gem takes 12*10=120 hours, so replacing 3 gems for super gems takes 360 hours in average.
totally we need 8+24+48+360=440 hours to max all super gems in mythic gears without using plat in average.
That is 18+ days.................
above only base on the chance of super gem being 10%
now do another math,if the chance is 5%
we need 8+24+48+720=800 hours which is 33+ days