iirc, a more reasonable idea was for us to either calculate the
physical attacks it does, as these are done in seconds and multiply that by the year charges. Another idea that
PowertoScale made was we use
Mechmaru's output in his regular mech and multiply that by the years as he does that in a second as well.
Ultimately though I think the hardest hurdle as many have pointed out, is we simply don't know the energy it takes for moving. The 6 days counter never decreases from any of his movements, but he also doesn't move much. So it could be taking 45mins or 29mins or 1hr worth of cursed energy to move and we'd never know.
The human walking speed is also unfounded. Just because it says activity limit, does not inherently mean, nor should we interpret it as implying that Muta made the Mech with the intent to ALSO operate at human speeds for a whole 17yrs. It was made with fighting in mind, not light strolls with Miwa.
But I do think either interpretation is fine. There's basically nothing explicitly stating one or the other. But, since there's not much to go off, the words used and what's meant for the mech suggest the activity limit is primarily gauging it's charges not overall.
"It uses that as it's field to mobilize it's
extra-large output" are implying this accumulation of energy is for the
extra-large output, unless we're to believe regular movements are also
extra-large output, which shoots down the idea of these regular movements being seconds of cursed energy usage.
"The more months and years charged up, the
greater the output." This is furthering the idea that the counter is for those charges, not for regular movement, unless we are to assume again that regular movements are relevant enough to take away from it. Also the panel shown is him doing the One-Year charge, not merely moving.