As a moderator, there are two ways to look at topics added over time.
1. In the Moderate area, go to the Topics tab and sort by Newest. This provides a list of all topics going back in time, with 25 topics shown per page:
2. In Admin > Reporting, the Activity dashboard shows the number of posts created in the time period you have selected.
I hope this helps! Let us know if you have any other questions.