It really IS basic:
Total amount of days between updates ÷ number of updates = rough average number of days between updates
As I said before, Team Echo updates the game whenever they feel it ready. A "rough average" does not play out here, because since 2021, updates took 1.5 -2 months to be here, while in 2020, they took ~1 month each (with the exception of 1).
So, your "rough average" is between 1 month (at best) to 2 months (at worst), which is a long time in between anyway.