I don't understand why you'd have Sunday end so early for a vendor that takes an entire week to farm the currency for to begin with. It makes no sense, and is very frustrating for people who can't access the game during the few days he is available. 9AM is a very arbitrary time for him to disappear, and all the more upsetting when you have been waiting an entire week to make a purchase. If you want to limit access to Xur put him at the end of a random strike every week that players need to hunt down. Just a random suggestion, and at least it doesn't screw people who don't work cushy weekday jobs. Or maybe extend him for the entire weekend rather than 9AM which is just a kick in the nuts.