Until' and 'till' express 'up to that time'. We use either the simple present or simple past with 'until' and 'till'. 'Till' is usually only used in spoken English.
- We waited until he finished his homework.
- I'll wait till you finish.
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We use until or till to indicate that something continues up to a particular point in time and then stops:
- Don't bother saving me any supper - I shan't be home till late.
- We had to stay in the exam room until the end of the exam. We couldn't leave early even if we had finished.
- I had no umbrella so waited until the downpour was over before I left the shop.
- We don't need to be at the stadium until the first race is over so we don't need to leave home till eleven o' clock.