As far as the credibility of the source goes, Mike Sampson used to run ScreenCrush and now works for Alamo Drafthouse.
According to a tweet from Mike Sampson, Fox has updated the runtime of Logan to be three minutes longer than what it was when it screened for critics earlier this week.
Adding just three minutes seems like a relatively arbitrary amount unless you consider that after-credits scenes are roughly three minutes long.
It makes sense that Fox would opt to keep some cards close to their chest and hide an end-credits scene from screenings for risk of spoilers.