The door just needs to connect to the timestream. It doesn't need to take uncountable infinite snapshots of a 4D timeline to do so.
I'm not seeing it embedding anything.
Context: The corridor has many names as is referred to as a spacetime, rift, and underworld.
Tau Star System is an alternate
dimension that is stated to be a region in spacetime. Saturn refers to the wormhole to the Tau Star System as the
corridor and Sailor Pluto uses the spacetime door to seal the Tau Star System away.
Chibi-usa says the past is on the other side of the
spacetime. (note: chibiusa is in the future, and sailor moon is in the past)
Wiseman's
domain is at the edge of spacetime. (Here's another scan where wiseman is in his domain and calls corridor the
rift)
When the cast uses the
key, they time travel to Sailor Pluto. This is described as opening a
route through spacetime. If the universes and times weren't embedded inside the corridor, it would a route to spacetime. Just as a route to the jungle, the route is not in the jungle, but a route through the jungle, the route is inside the jungle.
When Luna and Artemis are checking to see if there are any invaders from alternate dimensions, Pluto
confirms there are no invaders because there has been no disturbance in space time. Meaning the routes to alternate dimensions disturb spacetime, as previously established that routes are through spacetime themselves.
So in conclusion:
Alternate dimensions like the Tau Star System are regions in corridor, and beings can use routes that go through corridor to reach other dimensions.
Periods in the time exist inside the corridor and beings can use routes that go through corridor to reach other periods in time.
SO if you take a single snapshot of corridor, inside that snapshot you would include all the alternate dimensions and the routes between them and all periods of time and routes between them.