Good teaching moment for why estimates of big endeavours tend to be off, too. He appears to have slightly overestimated his average walking speed and greatly underestimated breaks (only some of which were by choice from what I gather).
The total journey appears to be 58,000 km (36,000 miles).
Expectation: 8 years, which translates to a daily average of almost 20 km (~12.5 miles). That's about 4-6 hours of walking time at my speed. Every. Single. Day. In sickness or in health, on country roads or through frozen wastelands. Seems optimistic even without anticipating any delays?
Reality: After 8 years, he had actually finished about half the distance, which I already find impressive. As of October, he has 2,213 km (1,375 miles) left. That means he traveled 55,787 km (34,664 miles) in around 27 years. That puts him at a daily average of almost 6 km (~3.7 miles), so probably 1-2 hours of daily walking time. That's actually not bad considering all the delays, but quite a bit less than anticipated.
New estimate: He expects to be home "by 2026", let's say January. Based on that premise, his new estimate is that he will walk 2,213 km in ~4 months. That's a bit more than 17 km (~10.5 miles) per day. Relatively close to his original, comparatively uninformed estimate, funnily enough.
All that said, I don't think I'd have the willpower to see this through, especially considering all the setbacks. Mighty impressive.