The timing is important going in both directions for the spirit realm. Our guideline is that everyone should be out with 10s left on the debuff (if possible.) We got our kill shortly after installing Gara'jalAnnounce
. This shaved crucial seconds off getting everyone into the totem ring, which is super important. It lines things up better when they come out (you need everyone out before the next totem appears), and it makes it less likely that the voodoo debuff changes targets to someone designated to go to the spirit realm (when this happens, it usually wipes us.) (I swear going in early gives you more time in the spirit world, too.)
Something I do as a druid is to hot the designated people before we change phases, while the dps are moving into place and breaking the totem. I'd guess as disc you could PoM someone and renew before changing phases. I doubt the health reduction can be absorbed, which is too bad for disc.