As Les said, how long is really a function of how bright it is, and what the reciprocity failure of your film is. There is no hard and fast rule.
But it is clear that you're learning the concepts. So let me encourage you to plunder in the archives and read up on exposure guides.
There are a lot of good references you can find with Google too.
But the important thing to keep in mind is that this stuff is *NOT* magic. When you're starting out some things, different for each person, seem extremely complicated. But after a while it becomes clear.
I learned it; other here learned it. You can learn it. Nobody is born knowing this stuff. And almost everyone here will gladly answer questions when you ask.
Welcome aboard. And have fun.