No experience with ducks, but chicken eggs will still make a baby chook after a couple of weeks out in the tropical heat (so still fresh).
In the fridge at least a month (remember that, unlike US eggs, Thai eggs are not washed, so the bug-proof membrane remains intact).
Or shell them (separate white and yolk if you like) and freeze.
https://happymoneysaver.com/can-you-freeze-eggs-2/