Follow these steps to create your own custom game.
Pick one of the standard game types from the File -- Load New Game Type menu. This will load a base configuration for your game including clock behavior and score values. Pick General Game if none of the other standard games apply.
See the Editing the Game Type page for setting of Game Type Attributes.
Read the Time Controls Overview section of this Help document to understand how Time Controls work. Then edit the Time Control - Master Settings. Then Add and Edit the Periods .
Test the Time Controls by setting very short period lengths (say 5 second periods). Then run the game through each period to make sure it is working properly. For example are scores and remaining clock time being carried forward from period to period as expected?
Once you have it working as designed, save the game to file by File -- Save . Give it a file name that will remind you of the game configuration. Later use File -- Open to open the game. You can also Add to Favorites for quick loading, but always save for saftey in case you inadvertently lose the Favorite.