You can check this in the User List in Settings Center.
※ Regardless of which product you use, the "Last Login Date and Time" is updated when you Log into the Teachme Series.
Related: Check the Teachme Series User List (Web Browser)
https://teachme.jp/8/manuals/51250269
※ Only administrators and Sub-administrators can view the "Last Login Date and Time" on the User List screen.