My wild guess is 9 months.

Aeon may not have to rise to anywhere close to the current Dashpay marketcap for this to happen. Once long time DASH users realize that Dash privacy features are severely lacking and not catching up with the competition, prices will start to plummet as masternodes get sold

I think the Aeon and DASH market caps will eventually meet somewhere in the neighborhood of 25% of the current DASH market cap (after DASH falls 75% and Aeon rises to that same valuation). This is just my wild speculation, so make your own conclusion.