How to translate Acts 1:7-8

"But he said to them, 'It is not for you to know the times or seasons which the Father fixed by his own authority, but you will receive power when the Holy Spirit has come upon you and you will be my witnesses in Jerusalem, in all Judea and in Samaria, and unto the end of the earth'" (Acts 1:7-8, my translation).

And, and how to understand textual criticism of the bracketed ἐν.