On Thursday, March 31, 2016, Tesla started taking Model 3 orders. Tesla first started delivering Model 3’s to employees and then existing Model S and X customers. This increased to 1,550 in the December quarter, which continued to be to current Tesla owners. Starting around January 23 Tesla owners, who had not ordered on the first day, could start configuring their Model 3s. As I wrote above, Tesla received 180,000 Model 3 orders in the first 24 hours.

Source: Forbes March 23, 2018 21:45 UTC