Hi everyone

My girl is in season and I am taking her to the sire on Wednesday, which will be her 13th day.  I'm not doing progesterone testing this time as although her levels were too low  last time, we mated her on day 13 and she had a litter of four on day 61.
I have no real concerns about the mating etc as I am using the same sire as before which belongs to a breed expert and someone who has been breeding for many years.
Plus i have lots of experience in this forum
What I AM concerned about is for the last two litters, the water bag was out for quite some time with no progression.  The first time was 2.5hrs before I called the vet and the second time I decided to be brave and waited 4.5hrs.  My girl had been panting and digging for some time but not pushing at all.  Both times the vet gave her oxytocin and she delivered pretty much soon after.
What I would like to know is, how long would everyone else wait before heading to the vet?  Obviously, my concern is possible dystocia but non of the vets I've spoken to can give me a rough  time to wait or how long it could have gone on for. 
Has anyone else had this happen and if so, how long did you wait?