I did a 75 6 months ago. Put in required amount of BioSpira, Stess Coat. Bought an put in fish later that day. Had no problems. Next day Ammonia and Nitrites were "0". These readings continued. Never had a Nitrate problem as I change 33% per week.
I have read that the bio spira takes hold in about 2 days, but I have always waited 2 week before doing my first water change. Of course, if your ammonia or nitrite were to go out of control that would be a different story, but mine never did.