Start with the view that the UK Royal Mail makes near-optimal use of conventional transport. RM has about 120,000 "front-line" mail staff (source: BBC about the recent ballot). Guess that half of these work in delivery, and visit every UK household on a particular day. Santa needs to do 60,000 8-hour shifts to do the same. That's about 60 years continuous 24-hour work to visit every household in the UK once.

The UK has about one hundredth of the global population, but is very densely populated, and has good infrastructure, compared to most of the world. The time spent door-to-door per household may be similar, but the distances between communities are much larger. There might be 100,000 isolated communities that can only be reached by trekking around Tibet or the Andes or Yukon or the Outback, or taking a tramp steamer to islands. (You can't rely on a motorcycle or a helicopter - the local infrascructure to refuel and service is not available.)

Just scaling up the UK figure to the world population is about 6000 years. I would expect to multiply by a factor of 3 or 4 due the longer average journey between communities worldwide. So my ball park figure for Santa is 20,000 years, give or take an ice age.