
Well 3 weeks at least, but some bitches are fertile and attractive up to 4 weeks, which is where the advice about precautions, appropriateness, being fair to others has come in.
Only a dog will know if she has truly finished.So if she is the average bitch you should be fine, but it would be wise to minimise any chance of distracting other dogs that are going for testing, or the slight chance she may still be receptive (some of mine have been mated days 18 - 22) and a complete distraction.
As I don't own males I have this problem all the time, and if I have a doggy event when a bitch has just finished a season, for the benefit of others, I will keep her away from sniffing reach of males, will bath and/or perfume spray, and maybe even give chlorophyll tablets if it's within a week or so.