OK, it cycled off from the 30 minute timer & not from a t'stat cycle. Forget the humming contact block mentioned earlier. After thinking about it, it won't tell what I thought it would.
Give it a few more days & see what happens. 3 things will definitely happen if the element is bad.
1) the water temp will drop
2) when this happens, it will call for heat & pump should turn on to cycle
3) pump will not turn off because the water can't get up to temp
If it's the element & you want to change it, I can help you with it if needed. Someone as yourself that knows how to use a multi meter should have the skills to change a hot tub heating element. It's not hard, but there's some other parts associated with the element that will need to be inspected while "you're in there".
Keep me updated