Sorry to bother, but do you know if the Dreamlands Excursion Ritual interrupts rest (For the purpose of curing madness). If there's a better place to ask about rulings and w/e I'm happy to be redirected!
As far as I’m aware, traveling into the Dimension of Dreams--via ritual or via sleep--doesn’t interrupt a rest. If your true body is asleep for 8 hours while you’re milling around in the Dimension of Dreams, you’re still treated as if you’ve had 8 hours of rest. Even death in the DoD has only minor penalties upon awakening.
The Dreamlands itself has slightly different rules, however, being a semi-stable demiplane in the DoD. The biggest one that’s a thorn in the question you’ve asked is that dying in the Dreamlands causes madness, which is counterproductive if you’re trying to cure it. As near as I can tell, though, so long as your true body goes unbothered in the real world, your rest is not interrupted. Just make sure to have someone attending to you during your stay, because curing madness requires 7 days of uninterrupted rest!
The full ruleset on how the Dreamlands works can be found in Strange Aeons: Dreams of a Yellow King, pg. 16~17.
So, full admission, I wrote the above before I realized what you were actually asking. I didn’t want to discard the whole thing because it’s actually informative, but to answer your ACTUAL question: Yes. Yes it does. Rituals are lengthy and demanding, and even though the Dreamlands Excursion takes less than an hour to perform, it requires a constant march around a mystic staircase and deals 2d6 damage from the strain of entering the Dreamlands regardless of success or failure, interrupting your recovery and resetting your counter. You can still get those 7 days of rest while inside the Dreamlands, though, provided you don’t die or experience any sanity loss, and recall that time in the Dreamlands is highly morphic; a single night of sleep can translate into a stay of years within the Dreamlands, making it somewhat unviable.
