Available since: 7.0.0
Time complexity: O(1)
Returns the absolute Unix timestamp (since January 1, 1970) in seconds at which the given key will expire.
See also the
PEXPIRETIME command which returns the same information with milliseconds resolution.
Integer reply: Expiration Unix timestamp in seconds, or a negative value in order to signal an error (see the description below).
-1if the key exists but has no associated expiration time.
-2if the key does not exist.