[dudul]

That is incorrect. When you start a new job you have a few weeks to enroll.

However, you sometimes have to wait for the plan to begin coverage. Something like "after 30 days of employment", or "on the first day of the first full month of employment". These are indeed idiotic limitations.

Worst case scenario, if you are changing job and something really bad happens during these 2 weeks where you don't have coverage you can retroactively enroll in COBRA.