cheers s.m , i worked it out to be 57 days and posted in our clan forum but not on here ;)
the rules/help section needs updating though , this is a copy n paste:
This table enables you to know the list of your stallions and the prices proposed one covering.
Click on the price in the column "Waiting request" to obtain the list of the requests made for this covering. Choose if you accept or refuse the request.
A stallion has a limited number of authorized covering. He gains 1 right of covering per day starting from the 61e day after its birth and he loses 1 right for each covering done