Not sure about the mountain bikes, ask arkokal travel, if they have them.
The bus gaes to corfu town at around 7.30 in the morning, and returns around 3 pm.
You will find trips going some days from Arillas, late afternoon, returning at 9 or 10 pm.
Again, arkokal do the trips, as does Arillas travel.(I'm sure someone will know about the bikes.)