I think that we are talking days, not weeks, or probably that Teslas can have multiple teams testing various hardware and algorithms at the same time: Tesla plans on producing 500k cars per year from 2018. If all of them have this equipment, and they drive a conservative 10k miles per year in average, Tesla will gather data from 5 billion miles driven after a year. Next year they will have 15 billion miles. After 6 short years that will amount to more than 100 billion (B) miles accumulated.
For comparison, Google's self driving cars have driven less than 2 million miles until now and unless they team up with a car manufacturer or launch their own car, their project is soon irrelevant. I imagine this would only be accentuated as tech talent would prefer to work where their algorithms can be tested in a couple of days rather than where such test would take years.
EDIT: And just imagine how cool it is that since their cars drive all over the globe, in all traffic situations, under most traffic rules, in all conditions, and both winter and summer, day and night at the same time, a team can actually test changes to an algorithm on cars selected for certain conditions (500 cars in Minnesota's winter weather at the same time as 500 in Australia's summer, 500 during daylight in Asia at the same time as testing 500 driving at night in Europe, 1,000 cars in rainy weather, 1,000 cars in sun, 1000 cars in fog, 1,000 cars in snow, all within hours).
