And the play is definitely not for masons to reveal. Let me talk through this.
15 civs, 4 mafia (3.75:1 ratio)
5 civ masons, 1 mafia mason (5:1 ratio)
Initially was thinking masons should all just come out, accepting one of them was mafia, and tabling it for now to get to a 10:3 (3.33:1) ratio. However, if that happens, mafia has the option of starting to pick off masons and getting double kills. Yes, they could also decide not to do that because civs will quickly learn who the mafia mason is. But if they do pick off the masons, then in 2 nights and 1 day, 5 civs will have died and one mafia member. Win for mafia. Sure, the angel could start protecting some of the masons and hope he gets lucky on one which then slows things down a bit by saving one guy for one night but not a significant difference.
Now while those night killings are happening, we'd have the 10:3 ratio to find mafia. Assume two day misses (and the mason night kills and lynching of the known mafia on day 3) and your count is 8:3 after day 3, with another night kill making it 7:3. Civs can then only miss twice more (or 4 times in total).
Masons should stay quiet as long as possible, and only come out if it is clearly inevitable they are going to die, as we'd rather have mafia at least have to waste a kill rather than us double-lynching two civs.
tl;dr - If you are a mason, don't come out unless you or your partner are 100% going to get lynched. Then do it to at least force mafia to make the night hit and hope angel guesses correctly.