I'm so glad, somebody raises that question. It's Microsoft's fault that you have to write such a long question, because they created that inconsistent mess.
Everything started with Microsoft making cross platform + touch input the top priority for Windows 8 and future Windows releases. That brang us
a Windows experience that was consistent with Windows ...
The trivial answer is "as quick as possible".
The user experience research group NNGroup has some relevant information regarding load times. Most relevant to your situation is probably the following.
The 3 response-time limits are the same today as when I wrote about them in 1993 (based on 40-year-old research by human factors pioneers):