JMP wrote:I think it is not possible to have a completely accurate "estimate". Your firmware settings affect how acceleration is handled and that information the slicer does not know, it can only guess.
The material usage on the other hand should be quite close, if it is way off you would have serious over or under extrusion.
you can get pretty close by comparing a few predicted times and a few actual times, taking the average multiplier and then applying that to all future calculations. Repetier host for example allows you to enter a modifier (e.g. 1.5x) to the build time calculation which will then automatically be used when predicting build time in future.
It will never be perfect of course since different types of prints have different movements and accelerations etc, but it gets a pretty useable result.