I've never gone beyond 150 days before, so I don't know if there is a limit for waiting on an event.
Worst case scenario though (assuming there is a limit), you could set a yearly on_action event that checks if a flag was "had" in the previous year, then set a new flag that indicates what year of contruction you're in (clearing year1 flag on year2 and setting year2 etc...), and if the right year of construction aligns with the right type of pyramid (ie. year3 & modest), then fire the appropriate event (ie. 1026). The "had" version of character flags works up to 2 years for sure, because I have done it (but should work well further).
Beyond that, I think this surpasses my abilities. Hopefully, someone else will know.