Also, a gotcha for anyone else with a similar problem: if you use number() on a datetime that has not been successfully converted to a date, you can get a large integer that you might think is the number of seconds since 1970, but it’s not.
In the attached, it looks as if the intervals are calculated as in minutes! Sort of. In fact, the date—although declared as a date—is still a string, and number() seems to just strip out non-digits.
