No they are absolutely not. Ask Jon Skeet for example:

https://codeblog.jonskeet.uk/2010/12/01/the-joys-of-date-tim...

https://codeblog.jonskeet.uk/2019/03/27/storing-utc-is-not-a...

Or look at the usual falsehood list:

https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...

Some interesting ones:

A week (or a month) always begins and ends in the same year.

Months have either 28, 29, 30, or 31 days.

There is a leap year every year divisible by 4.

The day before Saturday is always Friday.