Man, 90 minutes is wild but I bet those bottoms come out perfect. I ran a small pizza shop years back and made the same mistake with my stone oven. 45 minutes felt like forever so I figured it was plenty. Nope. First pies always had that sad pale crust underneath while the top looked fine. Once I started giving it a full hour plus the difference was night and day. Heat soaks into that stone slow, the air temp lies to you.