The capitalisation of "o'clock" is something which comes up from time to time. Guess case uses "O'Clock" and there is generally support for that form, but there is nothing in the English guidelines (https://musicbrainz.org/doc/Style/Language/English) which really justifies it. Since this is a special case which is also reasonably common, I think it should be made clearer what our position is.

Number of tracks with various forms:

Others: space, hyphen-minus, prime, acute accent, grave accent

Previous questions/discussions about it:

• http://musicbrainz.1054305.n4.nabble.com/Capitalization-of-o-clock-td1087592.html
• http://musicbrainz.1054305.n4.nabble.com/CapitalizationStandardEnglish-clarifications-td1061474.html
• http://forums.musicbrainz.org/viewtopic.php?id=5349
• http://chatlogs.musicbrainz.org/musicbrainz/2015/2015-05/2015-05-08.html#T19-28-21-261118 (which is what prompted this)