Need to rent time in only one room

I am trying to make agreservations work for my purposes and wonder if I am fighting a losing battle or if I'm just not seeing the solution. My scenario is this:

I have 1 room that I parcel out 4hr. blocks of time (11am-3pm, 3pm-7pm,7pm-11pm) 7 days per week. I need to be able to group those time-slots (as units?). And I need to distinguish between Peak & Off-Peak slots (using unit types maybe? not sure). Unfortunately everything I've tried doesn't allow me to group blocks of time. My latest attempt at configuration was:

1. Category type: 1xRoom
2. Unit type: 1xPeak & 1xOff-peak
3. Unit: 3x4hr. blocks of time i.e. (11am-3pm, 3pm-7pm,7pm-11pm)

The problem with the units is that they can't group hours into 4hr. blocks. No matter how I configure the units the hours still display in the form in 15 minute increments. I had a thought that timeframes might work if they were not just determined by "days" but also offered "hours". That way I could create a timeframe that spanned 11am-3pm and just set the duration to infinity and create 3 of those for all three time-slots., but I don't know if that would work or how to even begin to do it.

Any feedback is appreciated. Thanks.