
The test is really accurate, however to get a good result from it you would be best to retest 2 days after the last test to actually get the accurate rise again.
For your vet to have said mate in 3-5 days the dog must have been at stage 2 so generally the dog ovulates soon after stage 2.
The new tests for some reason when stage 2 shows up does say mate in 2-5 days I think this is a new addition to the tests. Is used to say retest in 2 days only.
Often people dismiss the tests but that is generally because they have not been done correctly and enough of them. Often people do 1 or 2 tests and to save costs don't do anymore and not wait for the ready result but that is just guessing and not the problem of the tests. :-) I have had 100% success with them.
People also say go with the stud dog but I do know trained stud dogs that would mate almost anything and young stud dogs get very confused and can try to mate for 10 days around that time.