Take this for what it's worth, as this is my first year breeding as well.

I believe I have one girl who's had her pre-lay shed, and since that shed, she's been coiled in a perfect coil on the warm side and hasn't budged. I'm counting 27 days from that shed to May 1. The other two also shed at the same time, but are not displaying the same behavior, so I don't believe it was their pre-lay sheds. They are, however both very "paunchy" so hopefully they'll gift me with their next shed being a pre-lay.

Watch your females, if they hug the warm side in a perfect coil, then start preparing. If they don't, it probably wasn't the pre-lay shed - keep pairing them (that's what I'm doing).