That's reasonable depending on how the combat goes, but you'd probably have to eyeball it so as not to drown in specifics. Stabbing someone before they get to hit back probably doesn't make too much noise, but a sword landing on plate or a shield is noisy, but those represent only a small portion of "reasons you don't take damage", especially at low levels.
Now, the thing about a random-ass random dungeon, is that there's no guarantee that the other denizens CARE. Maybe that single troll DOES hear a fight break out with troglodytes, but the two have clashed before and so the troll has no interest in checking it out, but that might be a different story for the sound of new people clattering loudly down the corridor.
On the other hand, if we're talking a lair within a dungeon, where you've got 1dX gangs of YdZ beastmen, sure they should hear and come and help if a fight goes on long enough. Now, of course you can be a mercifel DM and imagine they do the old "did you hear something?" back and forth before finally moving over, and perhaps don't realize it's an emergency so they walk over slowly, but just like there's a penalty for loudly running through the dungeon, there's a bonus for quickly and quietly dispatching enemies.
But again, I think injecting any kind of rules is going to end up becoming a book keeping nightmare for any would be DM, so rather than offer concrete rules, DMs should take it onto themselves to say "boy, it seems odd that they can just run full bore through this populated dungeon" or "it doesn't seem right that these kobolds one room over just sit and wait for the players to kick open the door and fight them" and make something up that satisfies everyone at the table.
Going back to the every 20 minutes. If there is any reasoning with regards to "realistic" dungeons, I haven't seen it, but it's worth noting you'll average about 1 random encounter per 2 hours if you're looking for 1 in 6 every 2 turns. That to me seems like the kind of reasonable risk that will discourage things like taking the slowest, safest route or meticulously checking every room for secrets while still allowing some degree of use of time as a resource. This is all to say I think that 1 check every 2 turns, from a purely gamist perspective, produces a reasonable number of encounters and feels like a good default, but I have seen some adventures offer different rates of rolling in order to fit their aesthetic. Maze of the blue medusa recommends rolling every 10 minutes + once per new room entered and has a 75% chance of an encounter, but it's a very large and elaborate encounter table with mostly empty rooms, with the intent that room + encounter = interesting. By contrast, in ACKs (and, I assume, B/X), you have fairly spacious dungeons with ~1/3 empty space, so only running into someone else on the move every 2 hours sounds about right.