We ran it on March 5th last year which was like... a week after the ice broke. In February, I called the office during hours, 8-12, and asked what the conditions of the ice were a couple of times. I ended up going for the permit before the ice broke, but only after I was fairly confident the ice would break before my launch.
They granted me a permit before the ice broke but were sure to try to dissuade me.
I would recommend calling them and keeping on top of what they know before you make a decision on a permit. It may be prudent to wait until they have confirmed that the canyon is clear before investing in one, but once the word is out the Saturday launches won't last long just like in the normal part of the season.