TimePilot 2930-R iButton Solo Door Lock looks like it will work for you.
You can set users up with a PIN, an electronic key, or both, and optionally restrict to time-of-day.
Another option is to use a regular RFID reader, such as the Visonic VXS-5 (there are a lot of these on the market):
Looking around quickly, I don't see any units that support time-of-day restrictions. However, you can then add a regular plug-in or hardwired timer that cuts power to the unit (or just to the door strike) based on time of day.
I would imagine in the higher-end units (that support PC-based programming and can network several units together) you could find this feature, but the price goes up accordingly.
The downside is that this option means you'll have to use a physical key during the "off" times. The upside is fob-based readers like this are pretty easy to find, and extremely easy to program.
Note: I have neither used nor endorse any of these products.
I do think the TimePilot product seems like a better option though. It's probably simpler to install, and it's more functional (you can have codes/fobs that work at any time of day, and others restricted, and set up different restricted times for different people). The downside is programming time-of-day restrictions means punching in a ~30 digit code for each user.