Reply by KarasCoutureCakes

I’ve worked with simple syrup (SS) and cakes for a while and my go-to rule of thumb is this:

While soaking the cake layers with a pastry brush and SS, routinely gently press a finger onto the top of the cake layer… if it looks wet (but not pooling) and not dry and sponge-ish, you’re at a good level.

It’s important to routinely check different areas of the layer to make sure you have even saturation as well.
Just MHO : )

~Kara

-- Kara @ Kara's Couture Cakes http://www.facebook.com/KarasCoutureCakes