I'd guess your locale. Part of your program is likely using UTC while other parts use local time. That can cause quite a difference in time...leading to different dates.

Update: Here's a quickie example:

$ cat x.pl
#!/usr/bin/perl -w
use strict;
use warnings;

printf "%d/%d %d:%02d:%02u\n", (gmtime(time))[4,3,2,1,0];
printf "%d/%d %d:%02d:%02u\n", (localtime(time))[4,3,2,1,0];

$ ./x.pl
11/23 19:51:40
11/23 14:51:40
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