Should be fine for what you need.
The documentation says it goes down to milliseconds.
https://support.smartbear.com/testcomplete/docs/reference/program-objects/aqperformance/value.html
Although, you have to factor in the time it takes to find you visible object. How much time that will add is hard to say. It depends what you're searching, how you search for it, and possibly how busy the applications object model is.
If it starts any processes or services, it may be slightly quicker to check for those instead? Not sure. You'd need to have a play about with it and see for yourself.
I'll also add (as I do performance testing as well), that unless you are only running this application on specific, controlled, hardware, then such a measurement cannot be accepted as a global given anyway.
Because:
Run it on a high spec i7/SSD based PC ..... launch is super fast.
vs
Run it on an Atom based machine, clogged up with other rubbish installed, and running off a 5400rpm HDD, and the result will be much slower.
Of course, if you control the hardware, then fine.
Just a nitpick:
Application Launch vs Application visible are NOT necessarily the same thing. As Colin_McCrae, there are a number of hardware and environmental factors that could make a determination of when the application actually becomes visible on screen.
Personally, while the features are there, I don't view TestComplete as a tool for that level of performance measurement. It's helpful in keeping track of stuff that has specific requirements, but there's always a variability of error.
