[plt-scheme] Multitasking

I was wondering how you would manage multitasking with Scheme,
e.g:
adding some bitmap objects in a list with a delay of 2 seconds
and repaint the canvas showing the modifications in real time(?).

I thought about the timer% class which would
do a (send canvas on-paint) as a notify-callback but it didnt seem good to me.

Would it be better with (thread lambda() ....) ( which i don't really
understand ...) ?
Or is there a way to use events/handlers?
I didn't learn anything about events except for changing the canvas%
class in scheme/gui to cope with mouse events...