Maybe the closest answer is this:

At first, when it was era of php 3, there wasn't session in php.

So the library named phplib supported session. And its expiration time was 1440 minute - a day.

But after, php became supporting phpsession, but its time unit was not minute, second.

Almost every code of phplib about session was ported to php core, and some of them are still remaining.


This is why php expiration time is 1440s(24 minute).