PHP Manual: jdtounix

function jdtounix(int $julian_day): int

This function will return a Unix timestamp corresponding to the Julian Day given in julian_day. The time returned is UTC.

julian_day: A julian day number between 2440588 and 106751993607888 on 64bit systems, or between 2440588 and 2465443 on 32bit systems.

The unix timestamp for the start (midnight, not noon) of the given Julian day

If julian_day is outside of the allowed range, a ValueError is thrown.

Version	Description
8.0.0	This function no longer returns `false` on failure, but raises a ValueError instead.
7.3.24, 7.4.12	The upper limit of `julian_day` has been extended. Previously, it was `2465342` regardless of the architecture.

jdtounix