You might want to have your "main" class implement
runnable then load  the image  in the run() method. Put
a sleep(3000) at the end of run() then call new
Thread(this).start() in your constructor.

Now this is just an idea to get you started. The
implementation details are up to you. For example, you
might need a way to kill the Thread that you started
so you must store it in an instance variable.