When dealing with Aeroplan, it's probably best to call before converting any points to miles, to confirm that the website is not displaying phantom availability. At least in the case of Amex transfers to Aeroplan which are often instant, it's been reported that an Aeroplan agent can hold the desired redemption while you are on the phone if you are prepared to initiate the Amex transfer during the phone call. (I'm not sure how quickly Chase => Aeroplan transfers occur.)