I have experience with getting a Russian visa at the Consulate in New York, and I would assume the experience is simliar to what your brother will experience in DC.

The turn around time depends on how much he is willing to pay - I had to get my visa last minute (long story), so I paid the $300 fee for same day service and had the visa in about 2 hours. If your brother has more time, there are $100, $150, and $200 options which range in delivery time from 14 days to next day.

Getting to the consulate/embassy early is really important - I arrived approximately an hour before the place opened, and there were probably already 30 people waiting. Luckily most of those people were not waiting for the visa services department, so I was able to get inside with the first group of people.

There wasn't much support or assistance inside, so it's important your brother arrives with all the required documents, and has the paperwork already filled out. He'll need the application, an invitation letter, photos, his passport, and a money order or certified check for payment.

All in all, it was relatively painless, with the exception of the $300 I dropped for same day service. Again, this was all based on my experience in NY, though I would assume that DC isn't that different.