Tesla's received roughly 400,000 reservations for the Tesla Model 3 and is aiming to start volume production at the end of 2017, but if you reserve one now there's a good chance you'll get it by the end of 2018. Tesla CEO Elon Musk said during the Tesla Q1 2016 earnings call that now is a good time to place a $1,000 reservation:

What I would say to anyone that is thinking about ordering a Model 3: now is a good time to actually place your reservation, place your order, because you don't have to worry about placing your order and receiving it five years from. If you place your order now, there's a high probability you will receive your car in 2018. I'd really recommend that anybody who wants to receive their car in 2018 place their order very soon.

Tesla's upcoming Model 3 sedan.

Though Tesla plans to begin volume production at the end of next year and aims to build 100,000 to 200,000 units of the car in 2017 and hit 500,000 total Tesla cars produced in 2018, the window for reserving a Model 3 and getting it by the end of 2018 is rapidly shrinking.

The roll-out plan for the $35,000 Model 3 further complicates things, with customers on the North American west coast receiving the first deliveries, followed by a staged roll-out marching east across the United States and Canada, and then jumping to Europe an Asia. Oh, and current Tesla owners get priority placement in the queue, so if you really want a Model 3 early, you better buy a Model S or Model X now.