I just finished a glass of Papazian's recipe for Avogadro's Expeditious Old Ale that uses Muntons Old Ale and some Cascade for finishing. The recipe says that it will be ready in 2-4 weeks...depending on how expeditious you are.
After 1 week in the bottle it tasted like old crap.
After 2 weeks in the bottle it tasted like young beer...and old crap.
After 3 weeks (tonight) in the bottle it tasted like a decent, flat English bitter.