How many years of seminary are required for a priest?

I don't know.

That said I think the usual is a bachelor's in philosophy and a master's in theology or divinity or something. And some seminary courses, probably.

All told, the educational requirements take about 7-9 years, if you are just wanting a basic ballpark answer. Years in an actual seminary would be 1-5 depending on the candidate's previous education. So if for some reason you already had a bachelor's and master's in those areas, you could be a priest in 1-2 years, though it would probably take longer, just because why rush things?

Four years of graduate school and preferably at least two years before that.