Depends on the size of the animal but within 3 days the odor of death and the dead animal smell will usually become a bit stronger and then after that the smell starts to gradually go away.
And then once 10 days have passed since the start of the decay of the dead animal the smell should be completely gone or almost gone.
So expect the smell of the dead animal to last at least 10 days but sometimes it can take a few more days.
If possible find the dead animal and remove the dead animal to make the dead animal smell which is awful go away much sooner.