what is 'reasonable' in terms of a delay
isn't defined in current consumer legislation, and for good reason. The length of time a consumer should reasonably wait whilst a repair is carried out is dependent on the context - some repairs take longer because they're more complex, or because a retailer (who is primarily responsible for the type of repair you're talking about) may have to obtain parts from a maker, or even send the item back to the manufacturer for attention.
In general terms we all have an inate sense of what constitutes a reasonable wait - although degrees of patience vary somewhat from person - but there's no definitive answer.
I suspect.....nay, I know that your question is motivated by a personal experience. You've aired your views quite forcibly in another thread, and I don't see there's anything to be gained from soliciting opinions in this way - pursue your resolution in your other thread.