The two problems I can see that might occur are:
The timer may give up the ghost from turning on a reactive electrical load so many times. Most timers work best on pure resistive loads.
The pump doesn't look terribly reliable, but looks can be deceiving.
And, the 2 1/2th problem: electrical power interruptions.
I can't think of an easier or more simple way to do this, so you probably have a winner.