Why does the Bosch Exxcel Dishwasher exceed the cycle time?

My Bosch Exxcel dishwasher exceeds the prescribed cycle time on all but the quick wash.

I have cleaned the machine with the appropriate dishwasher cleaner and cleaned out the float chamber having taken off the left side.

The problem remains.

The timer seems to be working satisfactorily but mid cycle, it jumps back and adds more time, before moving on.

The problem first appeared a few days ago when, for the first time we tried to operate the timer delay to start the machine some hours later.

Whilst the events may be unrelated, the coincidence seems to point to a timer problem and not as we first thought a blockage issue.

Has anyone had a similar experience please?