A typical case of making something more complex than needed. They could have simply used a window of time specified as no less than 30 days and no more than 45 days. That would have solved the problem in an elegant and robust way.
Also here in (some cantons of) Switzerland, during the month of notice you have to give to get married, the names of the couple is published so that people can protest the marriage if they know it's not a legal one, which is for sure something some people can find odious but it's not done for moralising but for practical purposes.
Think of it this way: If bigamy was legal, you would still want to at least know if you were the only spouse or one of several. A lack of reliable and readily accessible records makes deception all too easy.
Marriage is a contract. Agreeing to a mutually exclusive arrangement only to find out it isn't is a problem, even if you don't think polygamy should be illegal.
I don't know what percentage of the time bigamists are deceiving their spouses and married to someone else "behind their back," but that's certainly a version of events that happens and it makes everyone involved pretty unhappy to find out they aren't the only one.
This is typically done by someone who travels for work. It was much easier to pull off before our current state of global communications.
Daylight savings time switches happen in the middle of the night, IIRC at 2am or 3am.
A month ends at the end of a day, regardless of the length of that day or any other day during the month.
The OP's request was to make it simpler.
With time, you often can't do that without edge cases.