Yes, you can. They said that penalties would apply from the moment the map select screen loads, but they haven’t implemented it that way. If you try to leave during map select you get the 5s countdown. But if you leave during assembly you don’t get the countdown or a penalty.
It seems safe to say that whenever there is no 5s countdown on the dialog then there is no penalty.
I’ve been leaving every flash/clash/push as normal and no penalties so far.