You can check the option 'Special double periods optimisation' when at least 80 % of the lessons you have entered are to be scheduled as double periods. Special importance will then be attached to scheduling double periods in the subsequent optimisation process.

Internally, this process halves the time grid and the number of periods for the lessons meaning that only single and half periods need to be scheduled during the run.
CAUTION:
Please ensure that there is an even number of periods defined in the morning in the time grid. If the time grid has a total of 10 periods per day, only 4 or 6 periods should be declared for the morning, and not 5.