Is it normal for leg tips to sag on a 1d18h33m print?

That droop on the leg tips is almost always heat soak rather than a cooling problem you need to fix. When a print runs that long, the whole part stays warm, and small overhangs like the last leg segment never get a chance to solidify before the next pass comes over. You'll notice it mostly on the outer edges because that's where the fresh plastic hangs with nothing under it. At double scale it can actually get worse in spots like that, since bigger layers keep the nozzle and the radiant heat going for longer over each area. Before your next marathon run, do a short test print of just one leg segment and watch the part fan. If it droops the same way in a 20 minute print, then it's a fan or speed issue. If it comes out clean, you know the long run was the culprit and you can try dropping the nozzle temp a few degrees for those thin sections or letting the enclosure breathe a bit.

On the pause question, I just let them run. My longest so far was 31 hours on a big articulated print and I slept through half of it with the camera on my phone. A pause mid-print means the bed and part cool down, and when it heats back up you can get a weak line or a visible ring at that layer, plus there's always a chance the part releases during cooldown and then the resume is junk. Not worth the risk for a print that's allready proven it can hold on.

One thing that helped me was putting a small desk fan a couple feet away blowing at the room, not the print, just to keep ambient temp down near the machine on long runs.

Kind of relieved to read this thread because I'm still on small stuff, printed a little articulated octopus a while back and the tentacle ends did the same wobbly thing. I assumed my machine was broken and nearly started messing with settings I didn't understand, so glad I didn't. Question for you since you went double size: did you have to tweak any clearances on the joints before printing? I keep wanting to scale my models up but I don't know if the tolerances scale with them or if everything ends up too tight and the joints seize.

Been doing marathon runs since the days when the only 'camera' was you hovering over the thing every twenty minutes. One habit I picked up: before any run over a day, I swap in a fresh spool and zip-tie the end of the old filament to the new one so the handoff feeds through clean. Lost a 20 hour print once to a spool running dry at hour 19, never again. Also second whoever said let it rip overnight, a mid-print pause on a big articulated part never worked out well for me back when I tried it. And to the octopus person, yeah I nudged the joint clearances up a hair at double scale, otherwise they fused.

Update: turned out to be heat soak, exactly like the first reply said. I pointed a small fan at the open side of the printer for the leg sections on a test run and the droop basically disappeared, so the cooling was fine all along. Also stealing the zip-tie spool splice trick before my next long one, that 20 hour failure story hit a little too close to home.