Flex time is added before and after the clock in and clock out. Flex within work hours (after clock in and before clock out) is regarded as “Flex -” and flex outside work hours (before clock in and after clock out) is regarded as “Flex +”.
The flex time intervals does not have to be proportional, but it is recommended that it is atleast similar for each of the end points of the work day (clock in/out). You can have +2 hours and -1 hour at clock in if you want. Example: “Flex +” 06:00 – 08:00, Clock in at 08:00 and “Flex -” 08:00 – 09:00. However the profile will look at the total hours of work (from clock in to clock out) to determin when to start flex time calculation. So in that case you should have -2 hours and atleast +1 hour at clock out.
A standard flex profile might look like this:

Some times a worker want to register overtime instead of building flex, then the switch code “Overtime” is registered and this will then swap the Flex + for Overtime profile type.