Waldo,
Does your question refer to the rate of descent in a glide as discussed above, or to the time taken to commence drift down following a single engine failure?
There is a JAR ATPL Performance exam question relating to the latter option. The answer to this question is that an aircraft will generate more drag when heavy than when light. So there will be a greater thrust deficit following an engine failure when heavy. This will cause a more rapid deceleration to drift down speed, at which point the drift down commences. So an aircraft will start to drift down sooner when heavy than when light. If you are studying for the JAR exams you can see this effect in the drift down profiles on pages 86 to 89 of the CAP 698.