I thought that my ducks were not on the nests for long too and seemed to spend long periods of time away from the nest but i was lucky enough for both ducks to hatch 12 ducklings each.My partner talked me out of taking the eggs several times as i thought the duck wasnt looking after the eggs, I just put it down to ducks knowing what they doing, but up to you, if you really feel you need to intervene then go for it, its for the greater good, the survival of the babies, good luck I truly hope it works out for you, its so gut wrenching waiting for the ducklings