For the ten days we can make the ten games, do we have to work on only one game per day and move on to the next the day after?

As long as you're not procrastinating or scope-creeping! If you'd like to make two games in one day to 'bank' some time for later games, go for it. But don't let yourself spend 3 days on your first game and plan to catch up on lost time later in the jam. Life's too short.