Dynamically Adjusting max server memory Between Two Instances

I’ve got one server with two SQL instances. The server has 128 GB RAM. - Instance 1 has peak load from 08:00–10:00 - Instance 2 has peak load from 14:00–17:00 Currently: - Instance 1 has max server memory = 70 GB - Instance 2 has max server memory = 50 GB - The rest of the day, both are nearly idle. Would it make sense to dynamically shift memory? give more to one instance during its peak while reducing it on the other? Any downsides to doing that with a scheduled script?