1 He'll be writing a letter at 7 pm tomorrow.
2. He will have written a letter to 7 pm tomorrow. // He'll finish writing a letter to 7 pm tomorrow.
3 When I'll come home tomorrow, he'll be writing a letter.
4 They were writing test from 2 pm till 3 pm.
5 They'll be writing test from 2 pm till 3 pm tomorrow.
6 What will you buy him for his birthday?
7 I'll meet you at the station at 9 o'clock. My train will have already arrived at that time tomorrow, could you come earlier?