You dont have to select "cash". You have to have all tasks done. If you are financing through tesla, you would then have to have applied for financing and gotten approved through teslas site. Of course, if you do this and delivery takes more than 60 days, they will likely have to run your credit again.
You have to have "the money" part agreed to before you are actually in line. If you dont select anything, you are not actually in line, so any time you are waiting before that wont count. If you go for 90 days without doing that, you will likely get your order canceled.
The easiest thing to do is select cash because it doesnt require any proof of income, etc. When you finally get a vin assigned, you can switch either financing through tesla, or work on your own outside financing.