$ awk 'BEGIN{print strftime("%T", 3600)}'
> 02:00:00

$ awk 'BEGIN{print strftime("%T", 0)}'
> 01:00:00

strftime([format [, timestamp]])
                 Formats  timestamp  according to the specification in format.  The timestamp should be of the same form
                 as returned by systime().  If timestamp is missing, the current time of day  is  used.   If  format  is
                 missing,  a  default format equivalent to the output of date(1) is used.  See the specification for the
                 strftime() function in ANSI C for the format conversions that are guaranteed to be available.   A  pub‐
                 lic-domain  version  of  strftime(3)  and a man page for it come with gawk; if that version was used to
                 build gawk, then all of the conversions described in that man page are available to gawk.

export TZ=MET-1METDST
date
export TZ=MET0
date
export TZ=ZZZ-19
date

$ TZ=UTC awk 'BEGIN {print strftime("%T", 3600)}'
> 01:00:00