Thanks very much for the responses and al the advice, guys!
However, my original question wasn't clear - what I really wanted to ask is:
Does it matter how long it takes to do a workout for a particular body part?
In the case of chin-ups, if, for example, you do a total of fifty in an hour, is this better than doing a total of fifty during the course of a whole day?
And, if so, why?
You could do sets of as many as you can manage reps, with as little rest between them as you can cope with
(for example, on one occasion I did chinups: 7, 6, 6, 6, 5, 5, 3, 3, 3, 4, 2 (50 total, in 55 mins))
OR this many reps over the course of a whole day. Would this be just as good? If not, why not?
With longer intervals between sets, you could probably fit more reps into each set before you couldn't manage to do another one with good form.