I will be in Amsterdam on a Sunday and a Monday.  There is a possibility that I could go on Sat as well.  Is there anything I would be missing out on if I'm only there on Sun and Mon?  Are museums/attractions open?? 
thanks!
Most all the main attractions in Amsterdam are open seven days a week. Not being in Amsterdam on a Saturday means that you will be able to miss a lot of British "hen" and "stag" groups drukenly wandering streets in the evening;)