Syntax
SECOND(howlong)
Arguments
 howlong (Duration)
Return Value
Number: the number of seconds explicitly specified by howlong if identifiable, or 0 if a second is not found.
SECOND(...)
is equivalent to (NUMBER(INDEX(SPLIT(TEXT(...), ":"), 3)) + 0)
when ...
is a Time value. See also: INDEX(), NUMBER(), SPLIT(), TEXT().
Examples
SECOND("007:14:21")
: 21
SECOND(TIMENOW()  "00:00:00")
: Seconds since the top of the minute; the current second of the minute. See also: TIMENOW().
Seconds in Duration
SECOND() merely extracts the seconds component from a Duration value; it does not compute the number of seconds the Duration value represents in total. To compute the total seconds comprising a Duration value:
(
(HOUR([Duration]) * 60 * 60)
+ (MINUTE([Duration]) * 60)
+ SECOND([Duration])
)

(HOUR([Duration]) * 60 * 60)
computes the number of seconds represented by the hours component. 
(MINUTE([Duration]) * 60)
computes the number of seconds represented by the minutes component. 
SECOND([Duration])
gets the seconds component.
Common Problems
SECOND(NOW())
(or any DateTime or Time value in place of NOW()) causes Expression Builder to complain, Parameter 1 of function SECOND is of the wrong type. The argument must be a Duration value, not a DateTime or Time value. To fix, convert a DateTime value to a Time value with TIME(), then subtract a zero time to convert a Time value to a Duration value: SECOND(TIME(NOW())  "00:00:00")
. See also: NOW(), TIME().