For yearling bucks, this is their first breeding season, and they tend to act more like teenagers, chasing any "tail" just because it is there.
The typical pattern hunters observe is yearling bucks starting to pester and chase does weeks before doe are actually entering estrus. The yearling bucks just haven't learned that they are wasting their time. Older bucks know better. Often you can see a young buck chasing a non-estrus doe flat out, with older bucks slowly following behind, apparently just watching from a distance.
The older bucks don't waste effort on serious chasing until does really do enter estrus.
But to answer your original question, during her 24-48 hour estrus, a doe is usually mounted/bred on average 4-6 times. And all of these mountings/breedings can be conducted by different bucks (one DNA study found 27% of twin fawns have different fathers). Quite often these different mountings/breedings are done by different bucks when the first buck to encounter the doe is low on the social ladder, and with later breedings done by a more dominant bucks as they encounter the "action."