Pay attention to the stated requirements.

How can I get yesterday's date from today's date, but making sure I don't get weekends for yesterday's date.

my @is_business_day = (0, 1 x 5, 0);
SNOOZE:
while (sleep 86_400) {
    my $wday = ( localtime )[6];
    last SNOOZE if $business_day[$wday];
}
my $prev_business_day_datetime = time; 
sleep 86_400;
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This code is untested.