The major patches tend to be about 19-20 weeks apart specifically, and this has been consistent through Endwalker and Dawntrail, with the gap before the expansion release being much longer. So that would put it at the 5th or the 12th of August.

So 7.4 would probably be around 16th, 23rd or 30th of December. Which may have a further delay due to the holidays - although, they didn't bother with such a delay for 7.1's content.