1.when you use 回 , you should add a place, like back to school 回学校, back home回家
回来,means, somebody come back where you are, we usually use it as 从..(a place)..回来 means come back from where
2.it is correct.
3.you can say it in that way, but the common way is 十点三十五分。
4.钟(时钟)/分钟/秒
5.半夜or午夜。
hope my answer can help