I'm not exactly sure what you mean by this?
Could you give an example that is closer to an in game concept? (And not so Zen monkish...)
One of the best examples I know of Time as a Game Resource is the boardgame
Thebes. The game works like this:
Each of you is an archaeologist. Assuming a 2-player game, you have 3 years worth of time to play the game, split into weeks. (So, 156 weeks). The board shows the map of Europe and the dig sites around the Mediterranean, connected by lines.
To move from Moscow to Warsaw (which are adjacent) requires you to travel over one line - one week. From Moscow to London requires 3 weeks.
At the locations, there are various things you can do: 5 dig sites allow you to perform a dig (1-12 weeks long) where you draw tiles from a bag hoping to find treasures and not sand. Various cards appear at locations giving you resources that will help you find treasure: knowledge, assistants, etc. These cards take additional weeks to acquire.
On your turn, you move and then take a card (or do a dig). This takes a number of weeks according to distance and the card, which is marked on a time tracker. After your turn, the next player is the one who has the most time remaining! So, you can take consecutive turns if the other players have spent a lot of time already.
All of this is set against the limited time you have in the game. There's this continual pressure: Can I afford taking so long to travel somewhere? Do I look for more knowledge or go for a dig?
It's perhaps the best example I know of using time as a resource. (Great game; best with 2 or 3 players, though 4 is still fun. Takes about 60-90 minutes for a game).
You can see Gary describing something like that in the AD&D DMG in his discussion of keeping track of Time. However, his discussion regards having several active groups in the game - something most D&D games don't have. The idea of time as a limited resource? It isn't there.
For time to truly be important, either it must be limited, or there must be other groups that have actions that take time and who can adversely affect the players if they complete their actions first. (Which is another way of saying the available time of the players is limited.) In AD&D, this has seen use in "The Assassin's Knot" by Len Lakofka, which has a timeline for the adversaries, against which the PCs must race. The James Bond RPG also uses villain timelines in its adventures.
AD&D 1e is interesting in that there are several activities that take up a lot of time, in particular training, wilderness travel and recovering from being revived from negative hit points. However, the game really doesn't have any structure in it that makes this lost time meaningful. Yes, there are aging effects, but most campaigns don't last that long. To get from 1st to 15th level may only really consume a couple of years of game time. Meanwhile, if you add in a villain's timeline, it actually adversely interacts with those aspects, especially training.
Honestly, to use Time as a Resource in D&D requires a much more strict structure than currently exists in the game. I'm not really familiar with Birthright, but I dare say that would have such a structure, likewise with the Dominion rules in the Companion ruleset of BECM D&D. However, both these rulesets are at odds with the regular activities of D&D play; it's not just a case of adapting one.
Cheers!