Can you provide more detail? Synthetic processing with Catalyst certainly takes time, but that's true of of all synthetic processing really. Even with the ReFS fast clone, which is certainly the fastest synthetic processing in the product, I see it take 15-20 minutes for ~10TB on a 100TB ReFS volume formatted with 4K clusters, so 100TB could easily take 3-4 hours even there. With Catalyst the synthetic processing is quite CPU intensive on the StoreOnce itself (at least in my testing) so there are limits to the speed any given StoreOnce can perform synthetic operations based on it's hardware capabilities.
With any synthetic processing, it's best to spread out the schedule so that different jobs perform the synthetic operation on different days of the week to minimize the overall impact. Catalyst is not an exception to this recommendation. If you can share more details of the setup, and some more statistics on what performance you are seeing for synthetics, perhaps there might be more insights that can be provided.