Website application (Wash U) without essays

VerdantZephyr

So I wanted to know if anyone has applied through a website based application like Wash U's before. I was recently invited to interview when I apply. I am interested in Wash U's program and responded that I would like to interview but I am still waiting on my CAS fee waiver to come through. They sent me the link to their website based application and asked me to apply there. I am currently still working on my PS and DS as well as waiting on LoR's. I am a super-splitter so they, along with my resume and grad school records will be very important. The website based application however does not ask for any essays except a Why Wash U essay. Has anyone used their site based app before? Do they later e-mail you and ask for the additional materials? My inclination would be that they would expect me to send them on pretty quickly and rather than allowing me to make a good impression in the interview while I prepare the rest of the materials they might A: want to know where those materials were and why they were not ready yet or B: go ahead and process the application without them. Both of those would not be ideal for my situation.

Does anyone have experience with this want to chime in? When did they ask for the additional materials? Was there a timeline to complete the application? I am inclined to email them directly but I need to be very careful not to sound either unprepared in the email or like I am putting them off for later because I am not actually that interested.