I’ve been having an issue with Excel 2013 (from the Office 365 Click to Run installer) for a while now that I finally decided to dig a little deeper on.
I found that when I was double clicking on a file from Windows Explorer to open in Excel, it would take 15-30 seconds before the application would appear.
However, if I opened Excel from the start menu, or through a “Run” command, it would appear instantly.
I tried many different things to isolate this issue such as checking conflicting processes, watching processmon, and eliminating the network as a source of problems.
Eventually I hit the right combination of google keywords and came across this post.
Based on that recommendation I disabled Cortana and immediately saw improved response times from Excel. Hopefully Microsoft fixes this bug in time for Office 365 integration with Cortana!