if you want to check how much time remains, this should work (at least on Windows, on non-Windows platforms, i'm not sure)
$seconds_remaining_until_termination = ini_get('max_execution_time') === "0" ? null : ((int)ini_get('max_execution_time'))-(microtime(true)-$_SERVER['REQUEST_TIME_FLOAT']);
gives you number of seconds until the script will be terminated due to the time limit. (tested on Windows 7 X64 SP1 with PHP 7.3.7) - or gives you null if there is no time limit.