Parental Controls - How do I use them

Wasn’t sure where to put this, so, i’ve got a 15 year old and 8 year old who share a bedroom and xbox, now, not for the first time, i’ve got up in the early hours to go to the bathroom and seen the glow coming from the boys bedroom, and last night (or rather 2.30 am this morning) there they are playing doubles on Reach campaign, so my question is, how do i use the parental controls to turn the xbox off at a reasonable hour, say 11 pm, as it’s my eldests exam year and he’s taking the p by turning it back on when myself and my wife have gone to sleep aswell as waking his younger brother up to play too which is now unacceptable,

any help appreciated!!! is your friend