# start of epoch
$ perl -MPOSIX=mktime -wle 'print mktime(0,0,1,1,0,70);'
0 but true

# before epoch
$ perl -MPOSIX=mktime -wle 'print mktime(0,0,1,1,0,60);'
-315619200

# "normal" dates:
perl -MPOSIX=mktime -wle 'print mktime(0,0,1,1,0,100);'
946684800

# how close do we get to 2**32-1 ?
$ perl -MPOSIX=mktime -wle 'print mktime(7,14,4,19,0,138);'
2147483647
$ perl -MPOSIX=mktime -wle 'print mktime(8,14,4,19,0,138);'
Use of uninitialized value in print at -e line 1.