What is the difference between Time - Backlog recorded and Time - Backlog end of period?
If you use the date field of Backlog recorded, you are aggregating data. The Backlog end of period looks at backlog count at the end of the selected period of time.
For example, this is the backlog count over a week for a random account: 10 backlog tickets on Monday, 11 on Tuesday, 10 on Wednesday, 11 on Thursday, 10 on Friday, 9 on Saturday, and 9 on Sunday.
If you use Time - Backlog recorded, the result is 70. But if you use Backlog end of period, the result is 9.
For more information, see this article: Explore recipe: Backlog tickets by month.