Nothing shows up, but you can see the upgrade list 48h prior if your upgrade hasn't cleared yet. Go to CO.com, check flight status and then click on the upgrade standby list tab.
If you want to improve your chances, get your status matched on CO using
this. You'll get Platinum which will get you above other 1Ks and GSs on your flight (
this is the order by which upgrades clear on UA and CO).