Hey everybody,

due to the cumbersome procedure of mounting the letus extreme adapter to the ex1, i wonder if it is ok to leave the adapter on for a longer period of time (of course with the appropriate support rod attached), or does the weight of the letus somehow damage the camera if it is on for too long?

thanks for your oppinion!

There's no magic answer to this. If you are extremely careful and keep it supported you might be OK, but remember its a plastic lens adapter ring with a lot of weight from the Letus on it so frankly I wouldn't leave it on because you probably can't be sure you won't accidently end up stressing the lens.
You're choice - safety vs hassle.

If you indeed only use your EX with the adapter, you can leave it on - but when not in use, I'd loosen the 3 screws that fasten the metal adapter ring to the weight of the adapter itself.

And of course, never pick the rig by the camera handle!