What is the function of 次 (ci) in this sentence?

Here “我一天喝一次咖啡” means “I drink coffee one time every day”, but if you omit “一次”, the sentence would sounds not only weird, but actually we can’t catch the meaning.
Because basically “一天” just means “one day”, but if there is “ XXX times” behind“一天”, then we know “一天” means “every day”.
And you could change “一天” to “每(mei)天”, then, the sentence ”我每天喝咖啡”sounds normal, because ”每(mei)天”means every day in any situations.
If you say “我有(yu/you)一天喝咖啡”, which means “one day I drank coffee”, and it might hint something happed on that date. And normally you have more to say after you say“我有一天喝咖啡”.