In NSM, firewall bandwidth/connection/interface, etc usages can be checked for up to 30 days. Here is how to check them.
1. Log into NSM, click on the firewall name:

2. Click on dropdown list to select "Monitor", then click on "Live Report", click on "Custom":

3. After clicking on "Custom", calendar popup window will appear. Select the time range (here we selected April 6 2am - 2:36am). Click on "Reload":

4. The graphs for the period of time show up:

Now you can check connection count, CPU usage (MultiCore), Interface Usage and Connection Usage.