Question

Without modifying the form itself, can we make the from only show for some specific time, say 5 minutes.

Answer 1

You could do:

Thread.Sleep(...);
theForm.Invoke(...);

But at it’s core, that’s semantically equivalent to using a timer. The only difference is that the timer will pick a thread from the thread pool and in the “sleep” case you’d have to allocate the thread your self. I would advocate that’s better to use the thread pool where you can, which means you should just use a timer.

FYI: You can use a timer without using a System.Windows.Forms.Timer control by using the System.Threading.Timer class. That would allow you to do what you want without having to modify the form.