You've sorted your teammates into groups and started filtering your reports by user group, but what happens when you assign groups to a project?
When a project is assigned to one or more user groups, the only users that can see the project (when adding a time record) are the users belonging to those groups.
If your team has a big projects list, creating user groups and assigning them to the projects these groups will work on is a great way to make it easier for everyone to find the right project when checking in with NikaTime.
If you are a NikaTime admin for your team and this sounds like a great idea, head to the Projects Management page and assign user groups to your projects by editing or creating them.