When I went last week (April 19), the security guard at the stage door mentioned there was some event happening upstairs so he didn't know how long it would take people to come out or who would come out. Just about all of the major leads did come out, though there was a long gap after Lilli Cooper before Santino finally did (just after midnight). Though it worked out for me because I got into a conversation with the people around me, and by the time he did come out there weren't as many people left so I was actually able to say a few words to him while he was signing without feeling like I was holding him back.
The stage door for me was a little hard to find, but as another poster mentioned, it's on the 45th street side right next to the breezeway, though on the other side of the breezeway from where the hotel entrance is. Though if you're having trouble, the people at the desk in the breezeway were really helpful in directing us.