I found this on TripAdvisor, which is dated November 2018:

M Club on the 15th floor is open from 6 a.m. to 12 a.m., daily with breakfast served from 6:30 to 10:30 a.m., "light snacks" from 11 a.m. to 5:30 p.m., "family and kids" from 5:30 to 6:30 p.m. and "cocktails drinks," including alcohol, from 6:30 to 9:30 p.m. It seems as if children aren't allowed after 6:30 p.m. Apparently, "shorts, sandals, flip flops, slippers, baseball caps, gym-wear or bathrobes" are prohibited in the M Club.

Also, platinums and higher can have breakfast in the restaurant on the 8th floor between 6 and 10:30 a.m.