
With a maiden dog it probably does no harm to let him mate a bitch several times in quick succession, as it will give him confidence.
Ideally the purpose of a mating is to increase the chances of a fertile mating. A healthy dogs sperm will be viable for around 5 days, but probably at it's best for about two days or so. A dog produces sperm constantly, and it is then stored. Obviously if you use him every day, there will be more sperm on day one than on day two, and subsequently, as stored sperm will have been used upo, and you are then relying on newly matured.
That is the reason that it is often advised to mate a pair every two days for as long as the bitch will stand. This will normally be say 2 or 3 matings over about 6 days. This protocol gives the dog rwo days to replenish his reserves, as the sperm from the previous mating would still be available in the bitch should her eggs be ripe on the days in between.
In practice if the pair are staying together, and the male frets to be with the bitch on the other days, it may be better to let them mate in between, as he isn't resting, but it is probably beter to aim for alternate days, and this is what most people do when travelling back and forth to the Stud dog.