The biggest abstraction in D&D is Time. One of the first complaints leveled at 0e combat is the one-minute round. Many assume that the single Roll to Hit (RTH) and the single damage roll after a successful RTH are an abstraction representing how masterfully the combatant performed in that time, and that the hits dealt represent various attacks and blows in those 60 seconds. This depends upon how you interpret the guides. Look no further than the ruling used for magic shields which spells out the chance to block a single successful blow (attack). Others assume in that round that the combatant has exercised all of his experience and know-how in positioning, parrying, exchanging harmless blows, side-stepping, and generally Errol Flynn-ing it up in order to arrive at the single important RTH representative of that one meaningful attack. Maybe so. If you subscribe to that theory it's hard to justify tactical positional modifiers in your game. In reading the OD&D rules over and over, I've come to the conclusion that there was only ever one attempt to strike the opponent per round. Take into account Missile fire. In one minute a skilled Archer could loose half a dozen arrows quite effectively, and probably empty his entire quiver with non-stop launching. Again, I maintain that OD&D melee assumes but a single attack per round. I know this flies in the face of the standard oe acceptance of abstract combat. The issue is not truly one of combat, but rather the time associated with it.
For another example of the abstract treatment of the passage of time in D&D, look no further than Movement rates. The D&D Turn is defined as two moves in the Underworld. Characters take two moves per 10 minutes, ranging in distance from 60 to 120 feet. That's a rate of 120 to 240 feet in 10 minutes. Those rates may be doubled when the characters actually run in a panic situation. Hardly realistic at all.
Outdoors in the Wilderness (defined as unexplored areas, cities and castles; basically anything not in the Underworld itself) these numbers are tripled; a slightly more palatable 120 yards to 240 yards in 10 minutes. Not quite realistic either, although once in the light of day on the surface play normally becomes what is now known as hex-crawling; each Move constitutes one Turn which is equal to a single Day. But you get the idea. Don't let anyone tell you that glossing over Wilderness travel isn't old school. It was designed with the notion of rapid simulation in order to bring the player characters to their destination.
Take the rules for Surprise as another example of this abstraction of time. Surprise awards a free move segment or action, which can be taken to attack if the surprised foes are within range, and then a round of uncontested attack. If close enough the non-surprised combatant can use its free move segment to attack, followed by its free melee turn; that's two free attacks before melee proper begins. That's well over 60 seconds of attacks prior to a response by the surprised side.
Turns in 0e are so ingrained in the war gaming philosophy which gave birth to D&D that the original scheme was readily accepted, as it should continue to be. The fact is that time in D&D is all relative. It is based on Turns which begin at the high end outdoors in the Wilderness representing one Day, continue to the Underworld representing 10 minutes of movement or other non-combat activities, and end at the oft ridiculed one minute exchange of combat.
Does it really matter that a round (melee turn) is one minute long? Does it really matter that it takes 10 minutes to search a small 10 ft. section of dungeon wall? I think not. If you disagree feel free to adjust combat rounds to six seconds and Move Turns to two minutes, or whatever floats your boat. The simple Day-10 Minutes-Minute system is hard to resist for its ease of tracking. Yes the Move Turn could be changed to five minutes I suppose, but the abstract method first devised works very well if you employ it as written. When you keep it at 10 minute Turns, the characters are allowed five Turns before rest, thats 10 Moves followed by one Turn of rest, or one Hour. The Wandering Monster check is easy to track as well; in 0e it is made each Turn, or every 10 minutes.
The length of the melee turn is almost irrelevant. Whether an encounter takes 2 rounds or 8 rounds, referees will simply restart the clock post melee in most cases. So does it matter that 12 seconds or two minutes have passed? Downtime after the encounter normally rounds out the start of the next Move Turn. In my games combat normally represents 10 minutes. With 0e you almost get the feel that combat pauses the Underworld clock and moves to an abstract measurement of time in which sides simply take turns whacking at one another until the encounter is over and everyone has licked their wounds before restarting the clock once again. It's a fairly tight and simple system if you can accept the fact that it is nothing more than an abstraction and that the varied-duration game turns are all relative.
To recap, that's 10 Moves in 5 Turns, with 5 Wandering Monster checks, followed by one Turn of rest and a final Wandering Monster check. One Hour has passed. It is a simple and easy to remember system for tracking time in the Underworld. Each encounter will expend another Move Turn for every 10 exchanges of combat, or portion thereof. A typical Underworld expedition will embody up to 10 hours which includes all time spent underground and the return trek to the surface. Adventurers not resting as required, or surpassing the standard 10 hour allotment will become taxed or even exhausted.
Now we can stop talking even further about time with a few tweaks. Hours become Full Turns, and 10 Full Turns in the Underworld constitutes one Day. Other than the Day itself, all other references to time in the way of hours and minutes has been carefully removed. Suddenly we are returning to the table-top feel where time is all relative, or almost irrelevant. The true concern is using Turns wisely and effectively in the game Day.
To seal the deal consider this: All encounters which result in Combat expend one Move Turn; the first action being the melee itself, the second being rest and regrouping. Now Combat is merely the exchange of blows, each side taking turns until the outcome is determined.
I've whipped up a new PDF which considers the above information. It is now embedded in my OD&D links section to the right and is entitled Game Time.
EDIT: 3:00 PM EST: I made the changes necessary to the Time in the Game PDF. As a note, it does indeed replicate the OD&D rules with one exception; that all melee is considered to occur within the span of one Move (or roughtly five minutes for those keeping track).
I hope you find it of use. If nothing else it should help fellow fans gain a better understanding of the original system and its wargame underpinnings.
~Sham, Quixotic Referee