Why does he need to create a Horcrux immediately? Theory :

Each horcrux, even with Voldemort's modified ritual, is just a snapshot of Voldemort's mind-state at the instant the horcrux was made. What Voldemort has somehow managed using magic is to interconnect all these Horcruxes into a network, and build some kind of non-biological system to "run" his personality based on the snapshots.

This explains why he was able to observe the stars and think about his mistakes for 8 years until someone touched one of his horcruxes. Somehow, his network sends only the presentMindState to the body it hijacks.

This is how I assumed, previously, that Harry might defeat him. Since magic thinks he's got the same identifiers as Voldemort, is Harry is killed a moment after voldemort is, his mind should become the "top" element in the stack of memory states that is Voldemort's horcrux network. I would assume that he would have access to all of the knowledge in the lower states, but as the top, canonical state, he would have control when Voldemort respawns.

As it is, I'm guessing the respawned Voldemort after he's killed by magical resonance will lack the mind state changes since his last horcrux.