The time you choose can be different from when you enter, at least that was my experience. Perhaps they don't like it when you choose a quiet time and arrive when it's busy, but it's October and I think they won't care at all or even really notice.

The van Gogh museum is smaller than the rijksmuseum, but for me it has more interesting art that I end up thinking about and discussing with the person I go with, so you can easily be there 3 hours. Where you go depends on what interests you. For me van Gogh's art is way more interesting than most of what's in the rijksmuseum, but you could browse the collections to see what interests you more.

In the van Gogh museum it also describes the role that his sister in law, Jo, had. Without her none of us would know about Vincent. Definitely take some time reading about her in the museum too!

I’ve never been to the Van Goghmuseum, but the Rijksmuseum is (one of the) biggest in the country, with a varied collection (figurative art, household objects, over several eras). When I was there for about three or four hours, I didn’t have enough time to look at everything I wanted to see.

For any somewhat substantial museum I would generally recommend taking your time for one of them, instead of rushing through two. Unless you have a couple of very specific pieces you want to see, then it could work; but to me that defeats the purpose.