Interesting, I wonder what strange mix of stuff might be causing this. Office 2013 is kind of strange because it has to have all the subscription checks to see if you are entitled to use it or if your subscription has expired, it might be related to that.
But other thing I had noticed, which also applies at least to windows 8 and also to Excel 2010 is the following:
If you are debugging an application (it might be from visual studio or from delphi, it doesn't matter) and you are stopped in a breakpoint, then double clicking an xls/x file in the file explorer takes forever to open.
It happens as said also in windows 8, and in Excel 2010 too. It is interesting, because if you first open Excel from the start menu, then double click the xls/x file, it will open instantly. But if Excel is not open and you happen to have some code stopped in a breakpoint, it will take forever. I know it happens to me all the time when debugging FlexCel, and every time it gets some swear words from me.