Could you help correcting these sentences

Hello, guys. Again need some help with grammar and using appropriate tenses.

1) The pond has frozen. Boys are already(?) ice-skating.
2) Ice on the river had already melted, but there was still snow somewhere in the forest.
3) The boys quickly took the bicycle to pieces(disassembled?), cleaned all its parts, but they had been assembling it for so long that they didn't have any time left to ride on it that day.
4) The boys had been assembling the bicycle for more than two hours when their father came and told them that they had to disassemble it again because they had put it together(?) improperly (maybe, wrong or incorrectly?).
5) What have you been doing since we parted?
6) While we were walking from the station, he had time(managed?) to tell me about everything that has happened since the time of my departure.
7) Has Michael arrived? - Yes, he has been here for two days. He arrived back on Friday.
8) I decided that while I am living in the country house, I will take long walks every day.
9) The dinner had already been ready. Everybody had long been hungry but two guests hadn't been there yet.
10) The singer finished his performance, lights in the hall were going out, but the audience had not yet departed.

The most important ones - 3, 4, 8, 9,10. Or just help with the ones you like. Huge thanks in advance