Do you lack the creativity, skill, time, or talent to create a Megadungeon? Do you want a dungeon crawling experience that is epic in scale but without all the hard work? Then this rule is for you.
Instead of writing or making a full mega dungeon, write up and create vague “zones” instead. The zone may be each floor of the dungeon, or different areas on each floor. Perhaps the first floor of a megadungeon is an underground cavern that leads into an ancient crypt. The cavern and the tomb would both be one “zone” of the megadungeon. You describe them in open terms, sights and smells, and accompanying random tables, but you don't draw every room and corridor.
 Random Encounter
 Faction HQ or Monster Lair
 Hazard (Trap, Precarious movement, or dungeon “puzzle”)
 Landmark (Safe zone, unusual architecture, interesting tidbit)
 Snapshot or “Cut Away” Dungeon
 Stairs/Next Zone Passage
The reason why “hours” are used here is to make megadungeons feel big. Every turn for you is an in-game hour of exploring many side passages, large caverns, going through several transitional areas and sparsely populated dungeon hallways and side rooms. You might say these areas are smoothing over a more boring part of dungeon gameplay; retracing your steps, dealing with straggling monster encounters, climbing up and down walls that are not inherently dangerous; that sort of thing all rolled into an hour-long unit of time.
This means that you're still getting basically one encounter per hour. You also lose one torch every roll of this dice, indicated you've explored quite a lot of dungeon by then.
The “Snapshot” or “Cut Away” Dungeon is essentially where your players get traditional dungeon crawling among this otherwise abstract system. This snapshot is something the DM prepares in advance for each major area or place in the megadungeon. Essentially, a small to medium scale dungeon with several rooms, corridors, and tactical exploration and placement. The idea here is to concentrate your quality of dungeon making into these areas, so that you can have the “feel” of a megadungeon, without having to draw every single hallway and room.