Is there a minimum of time, which needs to be happening, for the {qaStaHvIS} to be able to be used ?

For example, can I say {qaStaHvIS wa' lup} ? Or do I need to use the {qaStaHvIS} only in reference to longer durations of time ?

I don't see any reason, for any restriction to exist, but I'd like to make certain.

qaStaHvIS wa' lup is fine.

The choice whether to use qaStaHvIS or not isn't about the length of the time period; it's whether you're setting a time that something happened or describing how long something took.

-- 
SuStel
http://trimboli.name