C<$return_by_hour> is an integer value representing the opening hour for the branch
=head2 get_push_amt
my $amt = $calendar->get_push_amt($date)
C<$date> is a DateTime object representing a closed return date
Using the days_mode syspref value and the nature of the closed return
date, return how many days we should jump forward to find another return date
=head2 addDays
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