Use the File Manager and go up one level in the directories (by default the File Manager opens the templates directory, click the little up symbol). Then select the logs directory. There is a login log that gives login data. Also the answer log gives student answers with time stamps so you can sort of figure out how long they were active. These are just log files. You might want to write a script to extract the info you want. Or you could extract info from the database, but that might be somewhat more involved.
Arnie