As tirwhan says, 86_400 is the same as 86400. Perl allows '_' in numbers, and it can appear anywhere in the number. Perl strips out the '_' characters in a number before using it. It is purely cosmetic for ease of reading.

   perl -e 'print 123_0_33_876,"\n"'
[download]

Copy and paste the above line for an instant demonstration. (If you're on Windows, you may need to change the quoting slightly)