It's until you get diarrhoea. If you have issues when taking Ascorbic Acid it would be a good idea to take it in a none acidic form such as sodium ascorbate or magnesium ascorbate.

BTW Ascorbic acid can be reacted with alkalines such as Sodium bicarb or my favourite, Magnesium Carbonate to form vitamin C salts such as sodium ascorbate or magnesium ascorbate. Magnesium carbonate does not react so well and needs a warm temperature and the amount of acid will affect the reaction. Making a bottle up in advance is a good idea.