If you add a profile group containing the standard profile and then the one covering the weekends I believe the profile group will be referenced on the login and find the additional profile. Not sure as it is not really my area, so you would have to try it.
See screenshot… use any of your current profiles and open saturday. Add standard time and start/end time. Ths will allow any employee in this profile to clock in/out without a penalty. Do the same for sunday and any other profiles.