I used to drink once a day too but I drank teh C kosong since teh is quite sugary. Maybe you can ask for siew dai / kosong also to cut down on sugar?
Once a day and not more than that should be fine as its within the daily max caffeine intake.
As long as you don't drink more than usual a day should be fine.
Not more than one cup. Is ok
1 cup a day okie