Although you may be able to find PIR sensors that run on 110VAC, that's because they contain an AC-DC converter inside the shiny white box. Very few plug loads run directly off of the AC; most convert it to DC.
It's much easier to design a DC circuit to accomplish what you're looking for, there are many parts and kits and design tutorials out there already. The adjustable timing feature really lends itself to a microcontroller application.
That being said, old plug-in clocks used the 60 Hz from the AC sine-wave as their clock signal to move the hands on the clock. You could try a similar technique, but be careful messing around with AC, I would still step down that 110VAC to 5 to 10V with a transformer or optoisolator... you want your circuit to be galvanically isolated from the mains power for safety. It would require a pretty complex DC register/counting circuit scheme to accomplish this, counting the 60 leading-edges per second for 3 hours. (https://www.maximintegrated.com/en/app-notes/index.mvp/id/1994)
Because of the long durations desired on the order of hours, a 555 timer implementation by itself wouldn't be accurate as transistor noted, since that is a 1 capacitor method. It could serve as an adjustable clock signal feeding into a counter circuit, though.
There are many ways to skin a cat here that can't all be discussed, and looking into the various methods is a fun way to learn a lot.