Okay can you please confirm if the user is logged in while she checks he course home page and see this duration ?
Note that the duration shown in the course details widget in course page shows the actual duration that is left for the user in that course .
Please also note here that if you have set subscription in course product (refer :
http://prntscr.com/c555wg) then for this uration student will be subscribed in course and system will disregard the duration setting in the course setting.(refer :
http://prntscr.com/c5567s) .
So disable the subscription duration in that course product .(refer :
http://prntscr.com/c556t4)
Note that above change will not take effect for the users who are already added to the course in past .
It will apply for the new users .
For old user you have to extend their subscription in that course from course admin.(refer :
http://prntscr.com/c557j7)