Pretty sure that's not the reason why time was so important in AD&D. It was important because when you leave to recoup or recover, the monsters organize and restock to be prepared for you when you get back. Guidelines in those adventures said this happens over a span of 1 to a half dozen days or so*. In a low level adventure that has thousands of gp of treasure in it, that 1cp meal at the inn doesn't keep you poor.Keep in mind that long healing times in early D&D were there to eat up time (the most valuable resource according to Gygax), which the characters have to pay for in lodging etc with an aim to keeping them poor and thus justifying more adventuring for gold.
*Edit: I'm starting Night Below tomorrow as a matter of fact, and in my prep reading, it's mentioned all over how monsters will react and restock when PCs have to leave and regroup and rest in town (the adventure heavily assumes PCs will do that fairly often or most assuredly have a TPK.). Speaking of, that's something much different from old school to new school. In old school, it was assumed you frequently retreated and went back to your base of operations. In 5e for instance, PCs are assumed to almost never do that, but to keep trudging forward. Imagine if in 5e you couldn't level up until you went back and spent weeks with a trainer?