Yair . . . wreckTX As far as I am concerned any change in rate opens up a whole can of uncontrollable worms . . . for instance when does night-work start, some specific hour or when you turn on the lights?
If I have a bloke work sixteen hours straight to get a boat to sea does he go onto extra pay when the sun goes down and the rate reduces when the sun comes up? Nah, just pay them a bit over the odds and look after them in other ways . . . foreign orders through the workshop at cost for instance.
There are lots of things can be done to provide a bit of incentive rather than stuffing around with rates, keep it simple I reckon.
Cheers.