For me, when I double tap or press the power button and leave it there, the screen will go back to sleep after 30 seconds. My old phone would turn off the screen after 5 seconds on the lockscreen. There doesn't seem to be a setting for this and it's just automatically set at 30 seconds.
Oneplus One 64GB (CM11S)
HTC Desire (MildWild 5.0) - Retired