Perl's flipflop operator is very useful for such requirements. This tutorial by Grandfather is an excellent primer.

The example code below allows for an arbitrary number of lines with an empty 'day' field, it reuses the last non-empty day field read.

#!/usr/bin/perl
use strict;use warnings;

my $day = '';
while (my $line = <DATA>) {
   chomp $line;
   my ($newday,$ptime,$stime,$ctime,$amount) = split /\t/,$line;
   $day = $newday if $newday..$newday;
   print "$day\t$ptime\t$stime\t$ctime\t$amount\n";
   }


__DATA__
01-May-2007     34      11am    567     665
        65      12am    657     4
        64      4pm     345     3
05-May-2007     87      10pm    987     56
06-May-2007     987     9am     8899    765
        567     unkn    4       3
[download]

This prints:

01-May-2007     34      11am    567     665
01-May-2007     65      12am    657     4
01-May-2007     64      4pm     345     3
05-May-2007     87      10pm    987     56
06-May-2007     987     9am     8899    765
06-May-2007     567     unkn    4       3
[download]