I've had the same thing. It's not helpful; when I said I would reboot later, I wasn't joking and I do not need Opus nagging me every 15 minutes. I will reboot when it's convenient.
Secondly, at the end of the session I shut the machine down. When I powered back up again the following day, Opus began nagging me to 'reboot in order to complete the install' again. I checked, and the version of Opus that was running was indeed the previous one, not the one I'd installed the night before. Apparently it doesn't recognise a power-down/up as being the same thing as a reboot! A reboot at this point fixed the issue, but you clearly have a bug there.
Finally, following the installation of a new version of Opus, on first startup it opens the 'what's new' page. This was bad enough when it opened it in the Opus help-viewer window - it now starts my web-browser to display an HTML page! Please get this stopped - if I really want to know what's new, I will go looking for it myself. I do not want my browser starting. Oh, and it also doesn't work - the page that is displayed is completely blank.