The ProQuest web site has a number of FAQs that answer many questions about publishing your dissertation. 

Here's what their FAQs has to say about how long it takes for a dissertation to be available once submitted:

• After you submit your manuscript, it must be approved by your graduate school before the site administrator sends it to ProQuest/UMI Dissertation Publishing. Once we receive the manuscript from your school, it can take 8-12 weeks before it is available online.

• (Retrieved from https://support.proquest.com/articledetail?id=kA01W000000k9pASAQ)

• Check out the links above for more information.