>> @@ -802,6 +810,9 @@ delete-pair
>>  				      (if (= (length p) 3) (cdr p) p))
>>  				    insert-pair-alist))
>>  	      (error "Not after matching pair"))
>> +	    (when (and (natnump delete-pair-blink-delay)
>> +		       (> delete-pair-blink-delay 0))
>> +	      (sit-for delete-pair-blink-delay))
>
> Why can't the delay be a float?

My mistake was influenced by the lack of the function that
would check for a positive number (e.g. 'positive-number-p').
I tried to find such a function, then noticed that 'natnump'
at least checks for a non-negative number, but I forgot that
this applies only to integers.  So below is a fixed patch: