Spund time

I had my  first  attempt  at spunding recently. Had transferred at the  right time to a purged keg and attached the spunding valve. It looked  good for a couple  days  but then lost  all pressure  overnight.  I had changed to a ball and spring with thumbscrew type from what I had built. The pressure  overcame the spring or the ball did  not  seat. Who knows.
I put my  old  setup of just a petcock for the valve that is manually opened. It looks like a car radiator drain valve. After it looked done I put on the co2 in the fridge.

The beer came out fine. I’m trying to time a Lager ferment to spund now and will stick with the old petcock. Any thoughts  on what day is a likely day to transfer for a Vienna  Lager using  WY 2124.