Can I wire a Bathroom Fan to two Switches in Parallel?
There's nothing electrically wrong with this, as long as no other part of the electrical code in your region is violated.  For example you can't over-stuff the junction box.  And your relay has to be rated for, and not get too hot, if used 24/7.

You can also do this with off the shelf home control components.

Note your ground needs to connect to the box frame and probably the timer frame, in accordance with normal electrical installation procedures.  The relay is is not touchable by humans and need not be grounded.