The Allies best time of early assistance was before the fall of Czechoslovakia which would have spread the Germans thinner and bought the west more time.

The British continued to have a small Army and the French were obsessed with defence as a strategy. I don't see how these two could have cohesively moved into Western Germany in any meaningful way - let alone managed the logistics of a protracted campaign. Germany also had a superior air force which would have made the Western advance even more costly.