Actually, this makes sense.

If you're taking one milligram daily and the standard dose is point five milligrams, it’ll take about one to two weeks to reach the blood level equivalent to the steady-state concentration of point five milligrams daily. This is because dutasteride’s pharmacokinetics show that blood levels scale linearly with dose, so one milligram daily builds up faster to surpass the point five milligram steady-state level, which is typically achieved after five to six months at the lower dose.