on my 4 night-a-week route, i fly (well...it has been averaging...) 8.5 hours a night, 3 nights a week and get a "short" night of 4.5 hours flying once a week. these are all "late" starts of 8pm local. arrive back home at 8am and it's away from the airport for 12 hours to do it all over again the next night.
flying is conducted in a lear 35 under FAA 135. using the company's flight time estimates for this route, i will have logged 1350 hours at the end of 12 months -- the limit is 1400 in that time frame.
at least you're getting a day off! i used to have 5 or 6 nights on followed by 1 or 2 days off and that was rough. it sounds like your company needs to hire more pilots.