It is accepted Halachically that one must wait six hours after eating meat before eating dairy. Some authorities quote the Rambam who says (Ma’achalot haAsurot, 9:28) “approximately six hours”, while others state that if six hours have almost passed and one is very thirsty and nothing is available to drink other than milk or a milk-based drink, he may drink it because in the period that the Halacha was established not everyone had watches, so many people could have made a mistake regarding a half an hour or so, and so it can be considered as if six hours have passed.