It's probably best to count the time after turn 2000 in time-consuming actions; that abstracts away the effects of bonus speed turns, air elemental form, riding a hasted spurred-on warhorse, etc, and is likely to apply whatever goal we aim for (except possible pure realtime, but it may be relevant even then).
To start with, we need a call to adjalign() with a positive quantity on or after turn 2000; on is obviously faster. There are a huge number of places it can be called, but all of them seem to take nonzero time. Thus, it's one action (the first on turn 2000) to gain enough alignment.
From the Quest to the Sanctum goes as Kerio has described, I think; unlock the quest (one action), teleport to the quest nemesis (one action). I'm far from certain it does cost one action to actually kill the quest nemesis, though; after the teleport, there would be an opportunity for a monster's turn if the monster had the right speed (I think; someone check me on this...), and a stray monster (not the player, not the nemesis) could potentially try to attack the player with a wand or similar weapon and hit and kill the nemesis by accident. It would be horrifically unlikely, but hey, that's what luck manipulation is for! From then, it's one action to move to and pick up the Bell (using autopickup); if playing a Wizard, the Eye could be picked up on this turn (any other class could, and would have had to, wish for it before turn 2000). One more action branchports to either the VotD or Vlad's Tower (as far as I can tell, it doesn't matter which); one levports to the vibrating square (requiring a lot of luck manipulation to land there directly rather than on the same level); then it's two actions for the Invocation (the Bell and the Book; I see no reason why the Candelabrum can't have been burning all this time). One more levport takes us into the Sanctum, next to the High Priest. Total so far: 9 actions.
I'm having difficulty conceiving of a way to kill the High Priest on the monster's turn immediately after the levport (if indeed there is one at all); as far as I can tell, there are going to be no other monsters in range except monsters that followed the player through the levports (which could have been carefully pre-lured to locations in the VotD or Vlad's to "pick them up"), and the monsters would have to get a turn then (is it even possible immediately after following?), attack the High Priest that turn (due to desire for the Amulet, tameness, or due to conflict), and actually kill the High Priest. (Alternative scenario: steal the Amulet from the High Priest and die in the same turn.) Potentially, we'll have to spend an action actually killing something right then, making 10. In either case, we'll need to move to and autopickup the Amulet, making 11 actions.
Next the ascension run. I'm assuming we luck-manipulate away the infamous "mysterious force", meaning that there isn't a need to be Chaotic here like there is in non-TAS speedruns (manipulating the Force away is equally difficult whatever your alignment; it's just the severity of its behaviour that depends on your alignment). The fastest way to go up, in terms of actions, is almost certainly the (rather boring and cheap) cursed potion of gain level. The minimum possible size for Gehennom (counting the Sanctum and Valley) is 20 levels, making 20 potions of gain level, and 20 actions, to rise up from the Sanctum to the Castle. An alternative method is to sequence-break, which works like this:
Sanctum (level 20) -> 2 actions -> real fake wizard's tower (manipulatable to level 18) -> jump onto the portal (1 action) -> bottom of Rodney's Tower (manipulatable to level 13) -> throw Amulet at wall (1 action) -> teleport Amulet (1 action) -> #sit or levport down (1 action) -> levport back to bottom of Rodney's Tower, landing exactly on level 13 and picking up the Amulet (1 action) -> 13 potions of gain level up to the Castle (13 actions). This is a total of 20 actions, the same as the other route, and would be a lot more impressive to watch. The upside, timewise, is that it skips 4 otherwise mandatory levels altogether, which would save the time the game would take to generate those levels, and also probably has slightly less text (and incidentally, works just as well given a non-minimum-depth Sanctum, because it skips more levels to compensate for more levels existing); the downside is that it requires considerably more luck manipulation to pull off. So far, this is 31 actions to the Castle.
From the Castle to the Plane of Earth, I see no reason why any strategy would be faster than simply using cursed potions of gain level on the way up (potentially landing exactly on upstairs and climbing those, to reduce the number of potions needed, or simply to reduce the very repetitive text). The minimum depth for the Castle is dungeon level 25, meaning 24 potions and 24 actions to reach dungeon level 1, and one more action to climb the stairs to the Plane of Earth if going up the conventional way (or one more action to drink the one last potion of gain level if going up the way DeathOnAStick so famously did by mistake). So the total number of actions from turn 2000 to the Plane of Earth is 56 (57 if the Nemesis can't be killed the turn he comes into vision; 55 if the High Priest can); the other thing to optimise, depending on the goal, would be the number of actions obtained per turn, which is pretty much independent of other considerations.
I'll try to work out the fastest route through the Planes later. Here, we're moving horizontally rather than vertically, which gives much more scope for creativity and thus makes it a lot harder to calculate.
