set-time-second!

[procedure] time-second time

[procedure] set-time-second! time integer

SRFI-19: Getter and setter of second field of a time structure time. See also make-time.

SRFI-18 and SRFI-21 defines time->seconds, and time-second can be used for it (not vice versa; SRFI-18/21 doesn't specify the epoch of seconds).