the exterior lights are regular incandescent bulbs right? flourescent and metal halide lighting systems are inductive loads, when a switch is used in an inductive circuit it is exposed to much higher forces than resistive loads such as incandescent bulbs. When the inductive circuit turns off the magnetic field around the inductor (ballast) collapses and trys to maintain the current that was flowing through it, in doing so large arcs can be seen across the switch, this large arc is extremely damaging to the minimal grade contact in these electronic timers. Is that enough said, or is it too much?

A lot of info there, I will look into them further, thanks