Currently you can only set one value for the working day (in hours) and that applies to all working days and all users in the workspace.
If the entire company is working 8 hrs M-T but only 7 hrs on Friday then the only option is to override the default working hours by going into each user's profile and putting 7 hrs for Friday. This can work for small workspaces but it will be time consuming for those workspaces with more than 50 users