After missing the museum on several trips to Thimphu, I finally went in. I had expected/been told it would take about an hour. Well - really - about 20 mins was plenty if you stopped and read. The examples of kiras and ghos is nice if slim. There was weaving going on in the back room - but ...I snuck a peek: you weren't supposed to go in!
As a tourist it is likely on your itinery - so go...but realize you have time for some emadatse with chia to spare.