Dear Joanna, Hortas museum is only open from 2 to 5:30pm Tuesdays to Sundays, so you don't have much option to time your visit. We went in Feb (low season), and arrived shortly before 2pm. We didn't wait long to get in. After saying that, if I were you, I would not go. Since you are only in Brussels for a few hours not a few days, it is best to stay in town centre. Hortas musuem is outside of the town centre, and you need to take a bus back and forth which would eat up your time. There are plenty of Art Nouveau buildings to see in Towncentre, including Music Instruments Musuem which has a restaurant on top. This is also next to the Musée Fin-de-Siècle Museum -dedicating to Art Nouveau. Both would be a lot more convenient for your visit. Honestly, Brussels is a city best enjoyed strolling around leisurely, soaking up the atmosphere, tasting their comfort food, window shopping through endless alleys of tempting chocolate and pastry shops and breweries. It is a city to experience its relaxed charm and not a city for "must see" tourist attractions hopping. As much as I have enjoyed Horta Museum, we went only because we were in Brussels for 4 days.