Can I change how quickly the curtain opens and closes?
Short answer: Yes. In Settings → Advanced → Junk Yard Edge Curtain, adjust Open delay and Close delay (about a tenth of a second each by default). Reset to defaults restores them.
Yes. Go to Settings → Advanced → Junk Yard Edge Curtain and adjust Open delay and Close delay. By default the curtain waits about a tenth of a second before sliding in — so reaching for the menu bar doesn't pop it out — and closes about a tenth of a second after your pointer leaves.
The curtain opens while you drag a slider so you can judge it live, and Reset to defaults puts everything back.