Thanks all, I think I like the idea of a PLC timer with mechanically interlocked contacts best, but in the end it is probably not priority 1 at the moment to evangelise either way.
Agree with RVSS for higher kW applications.
My new years resolution is to phase out imperial measurements, especially the mile, which I will be replacing with 1.852km, unless the person specifically tells me they are working with the international mile.
I am also going to assume metric horsepower, ie. the power to raise 75kg by 1m in 1 second under 9.80665 N/kg of gravity.