Started my first greater rift. I now know I am nowhwere near prepared.
I have noticed a yellow/biege bar and a purple one (progress)
I heard it was timed to 15 mins but I see no timer now the yellow bar is filled I just have to clear the minions and the bonus goal of the boss? Correct? I was running down the levels incase. There was a timer popped up on screen but both goals still remain.
It is 15 minutes, you can see the exact time left by doing a mouse over on the bar. Correct on the minions/monsters, but to grab the reward after beating down on the boss, you want to be 5 or so minutes up, or you're not going nail him before 15 is up.
If you fail on 15 essentially now you're just playing for the boss loot, the only way to level gems now is to complete on time.
There are far better guides to doing gr's than my simple explanation, look one up... if you want to go high up the numbers, you'll need to know all the tricks.