Depending on the exact size and complexity of the pocket dimension. It can be from Tier 3-A downwards.
3-A: Universe level
Characters or objects that can create or destroy all celestial bodies within a finite 3-D space at least equivalent in size to the observable universe via an omnidirectional explosion that covers the entire space, alternately create or significantly affect[1] a 3-D universe or a pocket dimension of comparable size, which does not involve the destruction and/or creation of space-time.
In this case, this tier basically speaks of our observable universe. Planets, galaxies etc without taking into consideration concepts like space-time.
A pocket dimension, normally, would be like this in nature. Similar to our observable universe.
However, some pocket dimensions would be far smaller.
Hence, from Tier 3-A downwards.
