Could you please check these few sentences? Thank you. It's urgent!

1) Though you are not a qualified Spanish teacher, I'll be happy to have conversation classes with you during my stay in Madrid.
2) I hope we can meet around 5 p.m. every day starting from 5 August.
3) I would be grateful to you if you could e-mail me your phone number, so that I can text you as soon as I know about your timetable.
4) How do you usually finish off a letter to a person of your age you have never met yet? (this is a real question).
5) As I wrote to you in my previous post, I'll get in touch with you as soon as I arrive in Madrid.
6) As I have a six-year-old child, it would be nice if you could devote half an hour to him every day.
7) He can only say a few words in Spanish but I would like him to use it in his everyday (?) conversations.

All of your sentences are fine.

I usually finish a letter this way:

Sincerely,

My Name

1) Though you are not a qualified Spanish teacher, I'll be happy to have conversation classes with you during my stay in Madrid.

This sentence seems fine grammatically. One thing to note is that "though" is used as a conjunction, so you might consider using a comma after it. Example: "Though you are not a qualified Spanish teacher, I'll be happy to have conversation classes with you during my stay in Madrid."

2) I hope we can meet around 5 p.m. every day starting from 5 August.
This sentence is grammatically correct. It clearly conveys your intention to meet at around 5 p.m. daily starting from August 5th.

3) I would be grateful to you if you could e-mail me your phone number, so that I can text you as soon as I know about your timetable.
This sentence is well-structured and clear. It effectively expresses your gratitude for the recipient's future action of sharing their phone number, and explains the purpose of your request.

4) How do you usually finish off a letter to a person of your age you have never met yet? (this is a real question).
The sentence is grammatically correct. However, when stating that a question is real, it is unnecessary and can be omitted.

5) As I wrote to you in my previous post, I'll get in touch with you as soon as I arrive in Madrid.
This sentence is grammatically correct. It conveys your intention to contact the recipient as soon as you arrive in Madrid.

6) As I have a six-year-old child, it would be nice if you could devote half an hour to him every day.
This sentence is grammatically correct. It clearly explains that you have a six-year-old child, and you would appreciate it if the recipient could spend half an hour with the child each day.

7) He can only say a few words in Spanish, but I would like him to use it in his everyday conversations.
This sentence is grammatically correct. It indicates that the child can only speak a few words in Spanish and that you would like him to incorporate those words into his everyday conversations.