You can, with one cavet. To understand it you have to understand that it has two stages. There's the "top" stage, where the top rolls from the front to the back. That you can stop anywhere you want. The second is the collapse, where it lets go of the back top end and folds down. That you can stop anywhere while you're stationary. Once you are moving > 5 mph, the top will force a collapse if it's part way down.
I've opened and close it at up to 70mph without a problem.