What do I do with the ground wire?
If the switch has no exposed metallic parts after installation&mdash;and has no ground terminal&mdash;then a ground connection to the switch is not needed.  Connect the three ground wires together (one from the power source, and two for the travelers).

If the timer has exposed metal, then there should be a ground screw.  If the junction box it is installed into is metal, ground the box by adding a fourth ground wire into the junction with the other three grounds, and screw the other end of the wire to the j-box.  Use metal screws to install the timer into the j-box:  This grounds the timer and was the standard way of house grounding up until sometime in the 1960s.

If the j-box is not metal, but the timer has some exposed metal, run a ground wire to it and fasten it securely somehow.  (Maybe add link to a photo of the timer for better advice.)