Is it normal for a first big multi-color print to take this long on the H3C?

Twelve hours for a mostly full plate with multiple color changes sounds right on track, honestly. I ran a similar job on my H3C a few weeks back, a big gray parts set with a few accent colors, and the time estimate crept up the same way yours did. The purging is almost all of it. Every time the toolhead swaps filaments, it has to flush the old color out completely before the new one starts extruding, otherwise you get contamination in the first layers of the new color. Gray hiding behind other colors means short flushes, but any bright or dark accent color needs a much bigger flush to come out clean. That little blob in the chute is doing its job. And no, the waste doesn't really shrink much once the printer has seen the colors a few times. The flush amounts are mostly tied to the color pair and how different they are, not to how familiar the printer is with them. There's a flush multiplier setting in the slicer you can lower if you're willing to risk a little color bleed, but for a display model I'd leave it alone. As for calibration, I skipped it on my first print too and it came out fine. The factory calibration is genuinely good out of the box. If you ever see first layer inconsistency or weird surface texture, then run the full calibration suite, but a perfect first layer means there was nothing to fix. You're not leaving hours on the table. If you want to cut waste on future multi-color prints, the real lever is print orientation and part placement so same-color regions print together, or shrinking the number of color swaps by printing the decal area as a separate small plate. That's saved me a few hours on big jobs without touching quality.

I have to push back on one thing though, the part about the flush amounts being tied to the color pair and nothing else. On my setup I've watched the same two colors behave differently depending on the model. A tall thin part with the accent color starting near the bottom flushes way more than the same accent printed as little towers at the end. There's some logic in the slicer that looks at what comes right after the swap, not just wich two colors are involved. So the printer does learn a bit from the geometry you feed it, which lines up with the placement advice being the real lever. I keep a sacrificial prime tower on anything with white in it and that alone took a chunk out of my purge totals.

One thing that helped my waste problem was swapping the flush chute for a small bin lined with a silicone baking mat. Sounds silly but those purge blobs pop off the silicone once cooled instead of welding themselves to the bottom of the chute, so cleanup between color-heavy jobs went from ten minutes of scraping to basically nothing. Also I tried painting the flushes into a tower once, the manual purge option, and honestly the results were mixed. Saved some filament on a two color job but bungled a three color one and got gray creeping into my yellow. I keep meaning to ask wether anyone here has had better luck with that than I did.