I have never used the spot timer on mine. When spot welding I do it by eye.
One thing to watch for is when the welder starts up on the button and welds for a few seconds and stops, stupid thing. This drove me mad until I realised that I had bumped the knob for the spot welder and set it to weld for those few seconds.
Halfwit 'mates' have been known to fiddle with it when visiting as well.
Chunko'.