I financed through USAA, and the person I worked with from Tesla swore that everything with the dealer funding stuff was done ahead of time.
March 31st rolls around, I go to pick up my 3 - a day I've dreamed of since I first heard of the Roadster - and I sign the paperwork. "THIS IS AWESOME! I OWN A TESLA NOW!" Not so fast... "Do you have a check for us?" "Um, no. Your people were supposed to get this knocked out with USAA." Three hours of anxiety later I finally was cleared to leave with my 3, but I'm fully convinced that if it hadn't been March 31st / end of Q1, I would've been sent home empty handed. During this time - a Saturday when USAA's funding department was closed - I and Tesla were on the phone with USAA almost constantly. I was told that things went very high up the management chain with Tesla about whether or not I'd get my car that day. My fiance and I just got more and more frustrated. I sat there with the key card in hand, being able to sit in my 3, but not actually put it in drive. Gave me plenty of time to go over every last thing on the checklist, but was an overall horrible experience.
When I was sent a survey about my experience getting my M3, I was very clear about how things went from being one of the most exciting experiences I've ever had to hours of torture and "Just get me out of here." I got a few different calls from Tesla apologizing for my experience.
Learn from what I endured: The funding department at USAA is not open on Saturdays. As someone else mentioned, they only take faxes, and as it's 2018 - Tesla doesn't have fax machines. Be very, VERY clear with both USAA and Tesla ahead of time about whether the funding request has been received and processed by USAA. Failure to do these things will likely result in all kinds of pain like I did.