I did a test leveling only with Method-zero after the nerf. Alliance side doing stockade runs from 20-58, then ramparts from 58-74.
For Stockades you just round up the entire dungeon, park just outside aggro range of the NPC guards, log to your lowbie, log back to your 110 and AOE. Rinse and repeat.
For Ramps you do the same thing, only slightly different. Round up the entire dungeon except for Omor(batman).
Park anywhere in the red, log to your lowbie, log back to your 110 and AOE. Immediately run to Omor and one-shot. Run out of the instance with both characters. Rinse and repeat. (If you're not carful to run up against a wall, some of the NPCs with their knockup attack will potentially throw your 110 out of the instance, off a bridge, or back down to the entrance, causing the whole dungeon to attack your lowbie).
Stockades will give ~30% of a level at level 20(with 50% exp heirloom buff), which slowly drops to 14% of a level by 57, and takes 2 minutes per run.
Ramparts will give ~30 of a level at level 58, which slowly drops to about 15% by level 80 and take 5-6 minutes per run.
With a 300% exp pot this should be retardedly fast leveling. Although several people have claimed that efficiently questing through low level zones while queuing for random dungeons as a tank or healer is actually faster. One guy in this thread said he reached level 57 in 9 hours flat doing this.
Given that you only get an hour of bonus exp, I'd probably use it during the ramparts phase. Level 20-60 is easy and painless and doesn't take much time, so no need for a potion there, and you risk wasting some of the potion buff due to instance lockout. Because ramparts takes 5-6 minutes each time(practice the run first before using the pot!) you should get the entire length of the potion buff with maximum experience per hour without hitting the instance lockout. And, for me at least, level 58-74 is the slowest part of the leveling process.
This is going to be more efficient if you have a guildy or friend(or dual box!) running you through the dungeon instead of using Method-0. If that's the case I'd maybe save the pot for the 90-100 range and just fly around grabbing treasures. You'd probably go from 90 to 100 before the buff ran out if you're super efficient.