Hey Greg,
Thanks for the response.
Last night I think I stumbled on a fix here. It appears that if you try to set screen and sleep settings in the new streamlined settings app, the above problem is present (i.e. Screen off time must be less than or equal to sleep time. Attempted to make screen off time greater than sleep time overrides the sleep setting).
I thought this may be related to the power plan, so I accessed the power settings in the older control panel app. Here, changing the plan settings allows for screen off time to be greater than sleep time, and it appears to carry through into the simplified settings app.
Thanks for taking the time to respond though! I have used longer sleep settings before, but the problem is my space as I'm in a apartment where my workstation is in my living room, and the fans whirring and screens glowing when I'm not using the computer is a a bit of a PITA :).
Anyways, looks like my problem is solved either way!