Can you make a very very fast demiplane with create demiplane?

Question

My goal is to create a Demiplane where I could craft, taking my time to do it, while time on the material plane would advance very very slowly.

Exemple : 1 year on my demiplane = 1 minute on the material plane

In order to do that, I tried to understand the rules but I am not sure on how to interpret the wording on the spells Create Demiplane, Lesser, Normal or Greater.

Create Demiplane, Greater : This spell functions as create demiplane, except the area is larger and you can add more features to the plane. You can use this spell to expand a demiplane you created with lesser create demiplane or create demiplane (you do not need to create an entirely new plane using this spell), in which case it has a duration of 1 day/level. Alternatively, when cast within your demiplane, you may add to your demiplane (or remove from it) one of the following features (or any of the features described in create demiplane) with each casting of the spell, in which case it has an instantaneous duration.

[..]

Features : Time: By default, time passes at the normal rate in your demiplane. By selecting this feature, you may make your plane have the erratic time, flowing time (half or double normal time), or timeless trait (see Time).

[..]

Time rates : Flowing Time : On some planes, the flow of time is consistently faster or slower. One may travel to another plane, spend a year there, and then return to the Material Plane to find that only 6 seconds have elapsed. Everything on the plane returned to is only a few seconds older. But for that traveler and the items, spells, and effects working on him, that year away was entirely real. When designating how time works on planes with flowing time, put the Material Plane‘s flow of time first, followed by the flow in the other plane.

The way I understand it :

• I cast Create Demiplane to create the initial demiplane
• I cast Create Demiplane Greater to add a time feature, selecting flowing time, specifying double normal time
• I cast Create Demiplane Greater to add a time feature, selecting flowing time, specifying double normal time
• bis repetita, until the flow of time is right for me

Am I correct? Is it possible?

Answer 1

No, the Create Demiplane spells don't allow for arbitrarily fast/slow planes.

The Planar Traits: Time section appears to assume that the Material Plane is the standard for the flow of time and that the flow of time on other planes are measured against the Material Plane's:

[Normal Time is] how time passes on the Material Plane.

One may travel to another plane, spend a year there, and then return to the Material Plane to find that only 6 seconds have elapsed.

The Create Demiplane spells allow you to "create a small, finite demiplane ... within the Astral or the Ethereal Plane". It doesn't allow you to create a demiplane within a demiplane, so no nesting shenanigans are apparently available.

Greater Create Demiplane allows only 5 options for time:

• Normal (the default, for which a casting of Greater Create Demiplane is not required; included for completeness only)
• Timeless
• Erratic
• Flowing: half speed
• Flowing: double speed

Since planar time appears to be measured relative to the Material Plane and there doesn't seem to be a way to nest planes (so: even if a plane's "flowing" time were relative to the containing plane, there's no way to create a new plane inside a demiplane with the Create Demiplane spells), those "half" and "double" speeds must necessarily relate to the Material plane.

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From a game balance perspective, this makes sense: it cuts off one major option for both PCs and NPCs to have infinite spells per encounter (as long as they can get to their "1 day there = 1 round on the Material Plane" demiplane, they can hop over, rest, recover spells and such, then return fresh as a daisy) or to send the "other side" to somewhere where they'd functionally be trapped for all time (eg., 1 round there = 1,000,000 years on the Material plane).

Potential Frame Change

If all you want is the ability to craft more quickly, talk to your GM about a custom magic item (or feat!) that reduces crafting time. IME, it's going to be a lot easier to handle "can craft quickly" than to handle "can restore all abilities and heal arbitrarily while off the battlefield for a round"; doubly so if the campaign doesn't revolve around hard deadlines.

Answer 2

Time changes from Flowing Time don't stack

This statement under the Planes rules is key to determining why they wouldn't stack.

When designating how time works on planes with flowing time, put the Material Plane‘s flow of time first, followed by the flow in the other plane.

In essence, Flowing Time is always defined as a rate of time flow in comparison to the Material Plane. Therefore, each time you recast create demiplane, greater, you would simply be restating a 2:1 ratio of time flow between your demiplane and the Material.