Did this happen once, or consistently with every project you tried to open? There's usually a re-scan of plug-ins that happens after the initial install that delays matters.
Also, I'm finding that delayed openings after a recent Windows start are not limited to SONAR. I opened Studio One to do album assembly shortly after starting Windows, and it took seemingly forever, which is not the norm. Even Open Office takes forever to find a doc if I don't wait for a while for Windows to do its thing. These days I boot Windows and do something useful for a few minutes, like wash some dishes or whatever, then come back and open programs.