Something like this (UNTESTED) should work:

my ( @buffer, @data );
while ( <LOG_FH> ) {
    if ( /(DATE_PATTERN)/ ) {
        push @buffer, [ $., $1 ];
        shift @buffer if @buffer > 8;
        }
    if ( /SEARCH_PATTERN/ && @buffer && $buffer[ 0 ][ 0 ] == $. - 8 ) 
+{
        push @data, [ $buffer[ 0 ][ 1 ], $_ ];
        }
    }
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