Should I have problems getting an F visa with a record of possession of marijuana?

I'm from Brazil, and I was charged with possession of marijuana on October 2006 in Washington DC. I came back for the trial and I was sentenced with 24 hours of community service, to be served in Brazil. I turned all my hours in time, along with a letter from where I served the hours. The person responsible for the community service hours talked to me on the phone and said everything was okay and all the charges would be dropped, although I never got any documents confirming this. Yesterday I applied for an F1 visa through the American embassy in Brazil in order to study Recording Arts in the USA. During the interview, the consul asked if I had ever been arrested. My answer was yes. He said that anyone with a criminal record should not be eligible for a non-immigrant visa. He said that there are wavers for these situations and that my case would be directed to Washington in order for them to approve, or not, the F1 visa. He also said that he did not know how long this process was going to take. What should I expect? What are the chances of my visa being denied? Should I get an attorney or wait for the result? Is it possible for me to speed up this process somehow? Thank you.