+1 on what Rich said.
I'd rather measure from ovy, if I catch it. I had a female shed twice after ovy, and laid 1 week after the second shed. I thought I had it mis-calculated, cause I was sure the first shed after ovy was the pre-lay shed. The second shed sure threw me off. Just shows me, though, that they all do their own thing. They'll be relatively close to each other in behavior, but there will always be big exceptions to the rules. And those rules are just guesstimated rules of thumb/guidelines.
Anyway, keep watch for about 5 weeks from now having eggs. (45-55 days after ovy)