These are the most frequently used opening hours for museums and other art related features in OSM. Apparently, most are closed on Mondays, or do not close any particular day: count value

263 Tu-Su 10:00-18:00

199 Tu-Su 10:00-17:00

186 24/7

175 unknown

144 Mo-Su 10:00-18:00

119 Mo-Su 09:00-17:00

110 Mo-Su 10:00-17:00

87 Tu-Su 09:00-17:00

67 10:00-18:00

63 10:00-17:00

61 closed

60 9:00-17:00; Mo closed

59 Tu-Su 11:00-17:00

52 9:00-17:00

50 Mo-Su 09:00-18:00

48 Tu-Su 11:00-18:00

43 09:00-17:00

43 Mo-Fr 09:00-17:00

42 Tu-Sa 10:00-17:00

40 Mo-Su 10:00-20:00

40 Su 14:00-17:00

39 Mo-Su 10:00-19:00

38 Tu-Su 09:00-18:00

38 We-Su 10:00-18:00

33 Tu-Su 10:00-16:00

30 “on appointment”

30 Tu-Sa 10:00-18:00