Given that the data source is a big text field from a database table, I wouldn't count on newlines as being a reliable guide for separating the entries. Better to use a capturing split with a regex that will match the date string -- especially if you know what "username" has to look like (e.g. all alphnumerics, between 2 and 8 characters, always starting with a letter, or whatever).

my $datex = qr/\[            # match open square bracket
                 [FMSTW][a-u]{2} \s  # match day of week
                 [ADFJMNOS][a-y]{2} \s+    # match month
                 \d+ \s+ \d+:\d{2}:\d{2} \s \d{4} , \s+   # match date
+, time, year
                 \w+         # match username (could be more explicit)
               \]:/x;        # match closing bracket, colon

my @text_blocks = split /($datex)/, $textfield;
my $initial_junk = shift @text_blocks unless ( $text_blocks[0] =~ /$da
+tex/ );

my %entry = ( @text_blocks );
print "DATE=> $_   STRING=> $entry{$_}\n" for (keys %entry);
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(update: simplified the part that matches the time field)