It looks as if they're defining a month as some amount of days. (30.4369, given the following.)
>>> 1 day + 1 month
1 day + 1 month
= 31.4369 day >>> 1 day + 1 month
1 day + 1 month
= 31.4369 day >>> 1 month -> seconds
= 2_629_746 s [Time]