Now, after starting Opera myself, sometimes, after a tad, I've seen Opera notify me (red dot in the top-left corner of the window) that there's a new update. Sometimes, I'll then goto the URL opera://about and Opera will check and fetch the update. Sometimes, the update has already been downloaded and finished and it's just waiting for me to restart Opera. I don't how each of those 2 behaviors are triggered though. The automatic download when Opera is running might happen when the scheduled task runs while Opera is open. I guess you could test this when you know there's an update by right-clicking on the task in the Windows task scheduler and choosing "run" when Opera is open. For just the red dot/red menu button notification itself, I think Opera might just be checking for updates when it starts up where it just notifies you, especially since the Opera autoupdate process launches and closes when Opera starts up. You could temporarily disable Opera's scheduled task and try opening and closing Opera multiple times when you know there's an update to see if Opera notifies you of the update. Also, there might be a difference in behavior depending on the update if Opera has a way to flag an update as critical and enforce it.

There might also be some differences between the type of install. I usually use an all-user install to "C:\Program Files\Opera" where the scheduled task is run as the SYSTEM user account, where a current-user install runs as my user account.

Note that for a standalone/portable installation at least, that doesn't have an associated scheduled task, it'll always update on you and automatically fetch the update with no problem when you start Opera without having to even goto the opera://about or opera://update page. It's so fast and certain that there's a command-line install switch mentioned in this post to not launch Opera after installing as it'll update on you when you don't want it to.

Anyway, those things have always been my experiences with Opera autoupdate.

If there is an update, Opera download it, do the installation and, when Opera is restarted, you have the new release running.