Add motion sensor and timer so either can turn on front lights
That can be done, but it's not a standard setup. 

The old-style solution requires a box somewhere with relays in it. The switch, timer, and motion detector are wired to the relays, and their controlled output contacts are wired in the appropriate combination to produce the behavior you want. That combination is then used to control power going to the light. You might have trouble getting a home inspector to approve this if it isn't done by a pro... and I'm not sure even then.

The modern solution would be to use home automation components.  Replace the existing switch with one that can be remotely controlled and that also informs the central control unit when it has been switched manually.  Install a motion detector that talks to the central control unit. Then set that controller's clock correctly, and program it to signal the switch to turn on and off in response to the proper combination of these inputs. Much easier to install, passes code, probably no more expensive after everything is accounted for, can be built upon if you want to do other fancy home  control later. RECOMMENDED  SOLUTION.