Hi ~ I generally start pressing down after I take the cake out of the oven and set it on the cooling rack but before I turn it out of the pan. So it's the first 10 min while it's still hot.
It's worked every time for me since I learned of doing this. Don't know about the WASC cake but don't see why it wouldn't work for that too.
Good luck!! 
I used this method the other day with WASC and the cake split on me. I used it anyway but just wanted to warn you about that. Even when usinig this method of leveling I usually have to trim something here or there for my cake to be perfectly level.
I use a kitchen towel and press down gently going over the surface several times. Then after 10 min or so I flip it over so the bottom becomes the top of the cake and it's perfectly level
I also squash it down immediately after removing from the oven. I use a cardboard cake circle that's a size or two smaller than the pan size so the circle doesn't get stuck in the pan and it allows the cake to puff up around the sides while flattening the middle.
As soon as the cake comes out of the oven I put a piece of wax paper over the cake, then a card board cake circle (or square or whatever size is the same as the pan) and then a ceramic tile on top. Squishes it right down. Works great for me.
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