Profile relations:
The profile relations can be used to dynamicaly change between profiles based on the time when the user clocks in. I use this for shift workers and also where they don’t have flexi hours but can work either from 5, 6 or 7.
The profile relations override the standard profile for the user.
dyntips.com by Fredrik Sætre 
HI Fredrik,
Very nice blog. For one of my customer we are implementing 3shift a day like 6am to 2pm & 2pm to 10pm & 10 Pm to 6 am and created profiles as required. But these users shift will change week by week these employees works as 6 day week. I wanted to create a profile group and attach 3 profiles so that according to the login it should calculate the profile. But when I am adding the above profiles in the profile relations with the above timings its not taking for the Night shit timings (10 Pm to 6 AM) as it says Start time cannot be less than the to time. Could you please suggest how it can be configured.
Thanks in advance.
Gnanendra.