When I was flying the B767 there was a directive that the centre tank fuel pumps should be turned off when the fuel quantity in those tanks reached 500kg. As far as I remember this was due to a possible problem with the pumps overheating if they were not completely covered by fuel. Unfortunately it was not always possible to get to the switches before the low pressure light came on and reminded you that you had forgotten to turn them off. As far as I am aware there were no plans to 'fix' the problem by having some sort of alert when the fuel reached the 500kg level. If you had to use your 'kitchen timer' for other things on an ETOPS flight such as setting a reminder to get the alternate weather on HF or plot your 10 minutes past waypoint check then it was very easy to forget to turn them off before they ran out of cooling fuel.