In the UK for example, daylight saving means 28 Oct 2018 has 25 hours (90000 seconds) so adding 86400 seconds does not increment the date

#!perl
use strict;
use Date::Parse;
my $epoch1 = str2time('20181028');
my $epoch2 = str2time('20181029');
my $secs   = $epoch2 - $epoch1;
printf "%d - %d %d\n",$epoch2,$epoch1,$secs;
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Try setting the timezone to one without daylight saving