HELP. Making space invaders, special ship spawning.

Hi gang. I’m making a space invaders clone for Uni and I’m working on the special enemy ship (the big one that flies across the top of the screen). Does anyone have a good work about for the random spawning of the enemy? example, during the game at random intervals the ship will spawn and move across the top and be destroyed by either the player or the edge of the screen.

It’s just a simple timer with a random time everytime it’s triggered. First at the beginning of the level and then everytime it’s triggered sets a new random time.