This depends on your settings.
Commissioners with their deadline set to the first game of the week will have their pick sheet lock all games when the first game starts ... even if it's an early game.
For commissioners with their deadline set to Sundays at 1:00pm ET, members must pick the early games prior to scheduled kickoff. However, they will be able to make changes to later games even after the early games have been played. For example, a member can go in and make a pick change on Saturday for a Sunday game, but would not be able to change a game played on Thursday at that time.
Please note that if your deadline is set to Sundays at 1pm ET, any early Sunday morning games will be treated the same as Thursday games.