I generally find executive lounge (Concierge/MClub) information - operating hours, etc. - is included under the hotel's "Rooms" tab for the Executive and/or Concierge Level guest room descriptions. C
For the Westin in Bangkok:
Bangkok Unique Hotel Room | The Westin Grande Sukhumvit, Bangkok
- All day complimentary tea, coffee and non-alcoholic
- Afternoon tea from 12:00 to 16:00 hrs.
- Complimentary Evening Cocktails from 17:00 to 20:00 hrs.