Benchmark: timing 5 iterations of FastMktime::caching_mktime, POSIX::mktime, TIME::Local::timegm_nocheck...
FastMktime::caching_mktime: 120 wallclock secs (120.21 usr +  0.05 sys = 120.26 CPU) @  0.04/s (n=5)
POSIX::mktime: 360 wallclock secs (165.42 usr + 193.81 sys = 359.23 CPU) @  0.01/s (n=5)
TIME::Local::timegm_nocheck: 293 wallclock secs (292.72 usr +  0.14 sys = 292.86 CPU) @  0.02/s (n=5)