That would take about 5 hours, depending how quick your step is.
Sounds like something id do, if I had nothing to do.

Go for it, but I’m guessing you have to walk back as well, so factor in the trip back, that’s 10 hours of walking, a little public transport time, carry the one...you could spend a a good 3 - 4 hours at the museum and still make it home by 10 pm.
You should leave no later than 7 am.

I’d suggest getting a bicycle, used and cheap, that would save you a ton of time!