# pay attention to MSwin32 doublequotes

perl -MTime::Piece -E "$t1=Time::Piece->strptime('23:58:59','%H:%M:%S');$t2=Time::Piece->strptime('23:56:58','%H:%M:%S');say $diff=($t1-$t2)"

121

# or directly subtracting

perl -MTime::Piece -E "say Time::Piece->strptime('23:58:59','%H:%M:%S') - Time::Piece->strptime('23:56:58', '%H:%M:%S' )"

121