You are talking about an alt-az mount, correct? The most common rule used is the rule of 500--expose for 500/focal_length_of_lens.
So if you are using a 50mm lens, expose for 10 seconds (500/50) to avoid star trails.
It doesn't matter (except to your mount) whether it's overloaded or not, since the mount doesn't move.
Totally out of point answer.
Please do not overload your mount. I repeat, do not. Hence, the question shouldn't arise. You already have the issue of field rotation to deal with. Leave it at that and be patient until you get a more capable mount, preferably equatorial.
One thing I can assure you is that the Orion nebula and Andromeda galaxy will still be there waiting.
Edited by kel123, 27 October 2019 - 05:45 PM.