Locking a game to prevent players launching it during downtime

Hey guys, Totally new here, so maybe a stupid question. Is there a way of preventing players in my game from launching it. Maybe they can only launch it if I as a DM have it launched? Just to be sure they don't move around tokens when the game's nog being played. Not that I don't trust them, but it feels weird to me that they can launch the game when the DM is not even active. Cheers!

Players can enter the game anytime, with or without the GM there. It is usually recommended that you create a landing or splash page which is just a map page that has an image or blank then put the player ribbon on it.

Yes, what Pat said.  The only map the players can see is the one that the player ribbon is on.  They also can not see any of the handouts you've created or monsters you've added until you mark them as visible to the players.  So splash screen stops everything except for their access to the character sheets and reading over things that you've previously marked as visible to them.