Student or Learner
I was standing in the cafeteria and having a word with my friends. Suddenly my manager came and asked whether I was going to spend whole day in cafeteria. AT that moment the time was 6:15 and our starting time is 6:30. So "it was still 15 to starting time or 15 minutes for starting time".
It was 15 minutes until your start[ing] time.
Here's how the exchange would go if this happened to me.
Manager: Are you going to spend the whole day in the cafeteria?
Me: It's 6.15. I don't start for another 15 minutes.
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