JTB FlexReport Detailed Reports can help you with this if you wonder why there are for example 7 licenses used in the middle of the night, or you might wonder about what users were using an application at a certain point when all licenses were used.
Set the filters like this for example. You don't have to specify start and end date because you can filter out that information later if needed. If you want a larger span you can set the start and end time between 00:00 and 04:00 as well.
Here are a couple of reports that shows you the result. One with checked out licenses that are not borrowed and one with checked out licenses that are borrowed.
Typically this is when an application does not return a license correctly when closed or it could be that the application is borrowed. Causes for this can be older versions of FLEXnet/FLEXlm or some bugs in the vendor application. One solution that worked for many is to use TIMEOUT or TIMEOUTALL. Even with that setting it will not help if the user left say AutoCAD running with a modal dialog box opened or a command in progress.
If you want to try JTB FlexReport a free trial is available upon request with full support without any cost during the trial period so you can make sure it works as expected.