Do the two week test.
Leave the geyser on for a week taking readings before and after then do the same but switch on and off and see if there is a difference in the readings.

I do not believe switching off for a period harms your element that much. it may be on its last leg anyway, but do make sure your geyser has the correct pressure control and vent valves to avoid unnecessary stress caused by the expansion and contraction on the tank.