Speaking to BBC News from his treadmill at the eight hour point, Mills was in good spirits, thanks to the combined effects of a five-minute break and a giant doughnut.
“I just stepped outside for the first time and it was actually great,” he said. “I’m going to do that more often, because I forgot there was an outside world.
“In here, in the studio, it’s like Vegas – it could be any time of day.
“Outside is grey, damp and cold, but it’s not in here, therefore the change of scenery was brilliant.”
However, he admitted he was starting to tire.
“My words are coming out and I’m not quite sure what I’m saying. But I’m still walking.
“Delirium will set in around 4am. Then, when I see Zoe Ball for her breakfast show tomorrow morning, I’ll be like, ‘OK, we’re good. We haven’t got long to go.'”
His co-presenter Jeremy Vine had other concerns, however.
“If the bosses see this,” he joked, “they’re going to work out we can power the whole station by running while we broadcast.”
