As far as I know you can overcure any gel product. It's more about how far you are going above the recommended curing times I suppose. This is just a guesstimation but I would think when gels are formulated they are so that they can withstand some over curing without compromising its integrity. Since clients hands can be exposed to natural UV light I guess that margin between curing correctly and over curing till the application is compromised is big. That said I'd say unless you are purposely curing the full set, you should be okay.
Not this is just my two cents and very much based on a logical premise not factual knowledge of the brand. You might wait for another geek to answer for sure or contact the brand/distributor.
While a great read (and the base of my comment) I don't think it answers the OP's question fully. However If they are using the correct lamp it begs to confirm what I said. Curing during the service probably won't over cure the product to the point it's compromised.
What I would add, now that I think about it is, why don't you just flash cure to set the layer lightly if the problem is the gel moving/shrinking? Then fully cure when you are ready. That should remove the possibility of over curing altogether.