Ran into an issue with strtotime() and time() this morning as the time changed back 1 hour.
date_default_timezone_set('America/New_York');
$expire = strtotime('+15 minutes');
if ($expire < time()) {
// session expired
}
Between the second 1-2am period, strtotime was producing times that were less than time(), so sessions were expired on creation. Why was that?
time() returns the current Unix timestamp, which, by definition is seconds since 1st January 1970, UTC. UTC doesn't observe time zones.
You're setting the time zone to America/New_York, then using strtotime() to get the current local time, which does observe time zones, hence the discrepancy.
UTC was specifically introduced to provide a consistent and continuous time reference. If you need to perform operations that rely on a consistent time reference, always use UTC.
FWIW, whenever I have to deal with time issues I set UTC everywhere (PHP, database, etc) and convert to local time in the presentation code - usually done by JavaScript on the client.