i am waiting for new one from cheesemaking.com which give the amount to use.
I am totally a beginner at cheesemaking, but one thing I found out is that the rennet reacts differently with different milks. The amount usually suggested on US rennet I suspect is for the practically manufactured milk one buys here in the store. I know this differs from milk sold overseas as I have been overseas and found out
So I would suggest that you go with what works and not with the instructions on the bottle.
I myself have a cow, so the milk I use is also different, and I use less than 1/2 the amount recommended on the rennet bottle as a result of testing the floc (I am sooo grateful to the folks here who have really helped me out!)
ETA: Also, I wonder if maybe you should be using "floc x" rather than a set amount of time, as before when you were doing it, you had a certain time you let it set, but your floc times differed. I am sure someone else would be able to explain that better than I can.