At the start of March earlier this year, Marvel surprised fans when it moved Avengers: Infinity War from its original May 4 release date to April 27, a full week earlier.
While no specific date is given, my guess is that just like Infinity War, Marvel would tack Avengers 4 at the end of the month, i.e.
It seems that the studio might be repeating that approach, as IMAX’s 10Q financial report lists Avengers 4 being scheduled for April 2019.
Assuming this information is true, whatever day Avengers 4 ends up hitting theaters next April, that means there will be less than a two-month gap between it and Captain Marvel.