The theory is that when the light comes on, the heater element has already been switched off, and will not come back on again until the temperature falls enough to trigger the thermostat to turn it on again. So you are operating on the residual heat of the boiler which will lose heat faster with no power input.
If you start just before the light goes out, you will be steaming with power on to the element, and it will stay on for a while, & keep the temperature up for longer.
It would probably take some trial & error to get the timing sorted, but in theory it sounds like it would help if you can get it right.
I have not tried this, so I offer it as a suggestion worth trying, rather than a tried and tested solution.