Look I don't dislike the idea of 12 being a clock, But I feel like 10 kind of already covers that aspect. Rather I had 12 be a snowflake due to 12-sided snowflakes existing, and also it being double 6. 12's gimmick is that if you uncover a mine, It will freeze your cursor, causing you to be unable to do anything for a few seconds. It can also freeze the water tiles, causing you to have to repeatedly click said tile in order to break the ice and select it. Be warned though, If this is done over a mine, It will explode if you click too much.
To Win, complete the board in time (frozen mines can be flagged, however the flag cannot be picked up afterwards so make absolutely sure it's a mine.)