Can you please check these sentences for me? Thank you very much in advance.

1)The meeting was held in spite of the rain.
2)In spite of the fact that/although it was raining, the concert wasn't postponed.
3) The meeting was put off because of/due to/owing to/on account of the rain.
4) I let you leave provided/providing that/on condition that you come back in five minutes' time.
5) You must stay here until your parents arrive.
6) By the time he arrived his parents had already left.
7) As she was doing her homework, the telephone rang.

1 is good

2 is in spite the fact that it was raining the concert wasn't postponed
3 any of those would work accept owing to. but i would put because of
4 on condition
5 good
6 correct
7 fine

#2 is better if it starts with "Although" and you ditch the "in spite of the fact that" wordiness.

Sure, I can help you with that. Here are the sentences you provided along with some suggestions:

1) The meeting was held in spite of the rain.
- This sentence is grammatically correct. "In spite of" means despite or regardless of. The sentence indicates that the meeting took place even though it was raining.

2) In spite of the fact that/although it was raining, the concert wasn't postponed.
- This sentence is also correct. It uses "in spite of the fact that" or "although" to express the same idea as the previous sentence. It states that the concert was not postponed even though it was raining.

3) The meeting was put off because of/due to/owing to/on account of the rain.
- This sentence is grammatically correct. It provides different options for expressing the reason why the meeting was postponed, which all mean the same thing - because of the rain.

4) I let you leave provided/providing that/on condition that you come back in five minutes' time.
- This sentence is correct. It expresses a condition for allowing someone to leave, that they must come back within five minutes. You can use either "provided" or "providing that" or "on condition that" to convey the same meaning.

5) You must stay here until your parents arrive.
- This sentence is grammatically correct. It simply states that someone needs to remain in a particular place until their parents arrive.

6) By the time he arrived, his parents had already left.
- This sentence is correct. It indicates that when he arrived somewhere, his parents had already departed. It uses the phrase "by the time" to show the sequence of events.

7) As she was doing her homework, the telephone rang.
- This sentence is grammatically correct. It states that while someone was engaged in doing their homework, the telephone started ringing. It uses the word "as" to indicate simultaneous actions.