So if you're editing your YC application in the application form (which I wouldn't recommend anyway), click regularly on the Save button at the bottom of the page.
We restart HN every 5 or 6 days, or it gets slow (memory leaks). Usually we do it at night and don't say anything about it, but since people might be editing YC applications, I thought I'd better issue a warning.
I haven't said when we're going to restart it, because I don't know. It shouldn't matter anyway; just don't depend on it.