How to Get There
In the Plan badge, select the Plan an Event options from the drop down menu.
How it Works
To assign hours, camping nights (and Boy Scout Miles), select the appropriate boxes in the first column of the Advanced Tab (Boy Scout Miles are not shown in illustration).
To Record Hours, Nights, or Miles, select the Record Attendance option from the drop down menu in the Plan Badge. Then select Attendance.
You'll need to place your cursor in each of the indicated boxes, like you were going to edit it, and then press "enter" to confirm and carry down the hours, miles, or nights all the way down the column. Note that this will fill the box of every user who was invited, whether or not they actually attended the event. If they DID NOT attend the event, they won't get credit for it, even if you enter a number into their boxes here.
Here's a gif of the feature in action:
Scroll down to the bottom of the screen and press "Update" to save your changed. That's it! You're all done!