1. I run 50 meters in 9 seconds.
2. I run for 50 meters in 9 seconds.
[Are both okay? Which one is commonly used?]
3. I sleep 7 hours a day.
4. I sleep for 7 hours a day.
5. I sleep 7 hours every day.
6. I sleep for 7 hours every day.
[Are they okay? Which one is commonly used?]
Since we're talking about distance, for the first group, only number one makes sense. Number two makes no sense because, 50 is related to time by the "for" instead of by distance by the "meters".
For the second group, I would say that number three is more common and informal, while number four is still common, but more formal. In an everyday conversation, you would be going with number three.