Five minutes is a really long time. It's long enough that my immediate suspicion isn't that any actual work is happening, but instead some sort of timeout is occurring. Given that you don't have any web code I think the most likely culprit would be some sort of database connection happening (or attempting to happen) on startup that it's waiting for.
I don't know what you ended up using for your DB handling, is it possible that Entity Framework or whatever else is initialized to have different behavior in debug or release mode? I'd look through your startup.cs or program.cs or whatever initialization with a really fine eye for any configuration differences based on the Environment.
I don't know what sort of logging you've implemented, unfortunately several standard solutions for that aren't fully initialized during early program initialization, but in cases like this you can hack in a temporary file writer to write out trace statements before the rest of your logging comes on line. It's not ideal but for this sort of thing I've done the same.