Hi,
Just courious as my friend has just had her dog mated, the thing is due to her bitch missing last time she had pre-mate test done so the vet said that she had ovulated on the 16th day so the stud dog owner due to going to a show could only fit in the one mating, and the dog that was used was used the day before would this affect his fertiltly at all?

No, I'm sure all will be well. :-)

Sperm from a good healthy stud should be viable in the bitches reproductive tract for at least 4 days and maybe a week.

If she was mated the day before ovulating the eggs would not have been fertilizeable until two days after ovulation, so 3 days after mating, and remained viable for another two days or so.  My self I would have wanted a second mating 4 or five days after the first in this case.