SECOND

SECOND —

SECOND (date)

SECOND converts a serial number to a second. The second is returned as an integer in the range 0 to 59.

Note that Gnumeric will perform regular string to serial number conversion for you, so you can enter a date as a string.
This function is Excel compatible.

SECOND(0.600613) equals 53.

HOUR, MINUTE, NOW, TIME.