I think as long as a sketch works, then surely duration is irrelevant.
The Two Ronnies used to do sketches that lasted several minutes.
In fact, I never saw them do any quickies.
Paul Hogan's sketch show in the 80s used to always end with a "him and his thick best mate" sketch that always lasted for about 10 minutes.
Monty Python sketches are renound for being more than a minute for each one.
They worked because there were gags going all the way through them.
Admittedly, the thing to avoid is padding your sketches with gumph, but if the humour and pace is there, why not have a longer sketch?
Thing is, quickfire sketches are surely more expensive as you need more sets, more costumes, etc.
For example, just imagine having to dress a set for a shop sketch (you know... ailes, products, counter, etc) for a sketch that lasted 20 seconds.
I don't think producers would allow that now. Way too much expense.
