Dranok's Temporal Study

You conjure an extradimensional apartment consisting of 3 rooms; a study/sleeping area, limited kitchen and a room for sanitary needs. The portal is of any and shape and size you desire (up to 10ftX10ft). This apartment is furnished to your liking though generally includes a writing/study desk, an empty bookshelf, a small bed or cot and a small table and chair. In addition to being outside the normal dimension of space this apartment is also outside the normal dimension of time. While in the apartment a person experiences the passing of time as normal, the rest of the world appears to move much slower. To everyone outside the extradimensional space  the person or persons in the apartment will seem to "live faster".

The spell requires to identical hourglasses. It is best if they are both full hourglasses, but it is not required. What is required is that they both track the exact same amount of time. After casting the spell, one of these hourglasses remains in normal time and space, the other is taken into the Temporal Study by the caster or the person using the space. The two hourglasses are linked. The hourglass taken into the study will remained temporally locked to its twin. Therefore, sand in the hourglass taken in to the study will flow at the exact same true rate as the other, which will appear slower to the person in the study. Giving them a method to judge how much time has passed in normal space and time. And their subjective difference from normal time. If either hourglass is turned over the sand in the other is automatically made to match that of the one turned over. 

From his writings, it seems Dronok developed this spell and its companion Temporal Extension to aid himself and other wizards in having additional time to study, experiment and investigate the arcane and other important factors, especially if there was little real world time to do so.

This spell is maintained by two separate methods.  Initially and primarily through the concentration of the caster.  If the caster remain in normal time and space and allows another to use the apartment then the caster's concentration is what maintains the spell. 

If, however the caster is the on inside the apartment , there is an additional safety measure. So long as there is still sand in the top bulb of the hourglasses the spell can remain in effect with only the casters presence, concentration not required. This allows a caster to sleep inside the Temporal Study with the spell maintained. Providing the caster resumes concentrating on the spell before the sand runs out. This allows a caster to sleep without ending the spell.

The spell can be maintained for a maximum of 12 hours, normal time.

When the spell ends all persons and all items they brought into the Temporal Study are ejected back in to normal time and space, at the portal entrance.

If any person inside the apartment reaches exhaustion level 4 the spell automatically ends. 

The amount of time dilation created by the spell depends on the level cast and is expressed in a ratio of subjective time in the Temporal Study to real time.

4th Level  -  6:1 (6 hours of subjective time for every hour of normal time)

5th Level  -  8:1 (8 hours of subjective time for every hour of normal time)

6th Level  -  12:1 (10 hours of subjective time for every hour of normal time)

7th Level  -  16:1 (16 hours of subjective time for every hour of normal time)

8th Level  -  24:1( 24 hours of subjective time for every hour of normal time, or 1 day subjectively for every hour normal time)

9th Level  -  24:1( Casting this spell at 9th level offers no additional time dilation above 8th level)