As Hive account@sebi99p pointed out, it only takes (13) weeks exactly to Power Down Steem Power into Steem, and you can have went to a different exchange.

Also, you have the option of going to the market within Steemit to convert SBD's into Steem immediately, so you don't necessarily have to wait (13) weeks to get fiat currency from your Steemit holdings.

Mind if I ask what happened when you tried to sell the Steem?

Lastly, "...the money is not itself usable," isn't an accurate statement. It has a fiat currency value at all times, and you're free to sell your Steem and take the proceeds out in USD's at any time. I assume that's the usability that you want.

I hope you get it worked out. I'm sure there's many here that would be happy to help you. I've never sold any Steem, so I can't speak from experience. I have used Bittrex many times however, and it's fairly straightforward.