Just had this experience at ATL two days ago - not on the way home from SXM but from another Caribbean destination.

It was a Tuesday evening (honestly thought lines would be shorter mid-week) - the mobile app stations were NOT being used - we have the app and asked if we could use them and were told 'no' - they were not in service at the time. Line to get to customs took every bit of two hours - actually it was two separate lines - one line to get to the front of so that we could be assigned a line to get in to. Customs was super simple - stand - show passport - snap picture - go - we weren't even asked to declare anything - not even the Cuban rum I had in my suitcase. Then to grab suitcase and recheck it which is also super simple - it's basically just grab bag from one conveyor and put on another conveyor - don't even have to talk to a person. Then back through security.

the whole ordeal took about 90 minutes to two hours - our flight was already two hours delayed. Many people on the plane badly missed connections. I did not as I know the hellscape that ATL customs can be and know full well that planes to and from the Caribbean are often delayed by quite a lot.

Having said all of that - for me flight planning depends on what I have going the next day. I knew I had to work on Wednesday so missing the connection was not an option - I'm a contracted employee so I don't get paid if I don't work. If I'm flying on a Saturday or Friday and I don't have anywhere particular to be the next day, I will book a tighter connection, but never less than two hours - and never if I have a big group in tow. If I really need to be home the day I am traveling, I book a connection of at least four hours. This one was supposed to be five.. As it was, we just barely made our connection and got home some time just after one am.... which made me a very tired girl the next day... but I got to work - and on time.

My next step is to get GE - we travel alot and out of the country a fair bit (mostly to the Caribbean for diving or sitting on a beach) - BUT that would not have helped us this time with five other family members in tow.