Never. Boveda is the only product in the world that knows when to stop adding moisture and won’t humidify beyond the RH on the pack, so there is no such thing as “too much”. Using more than recommended will just work more efficiently and last longer.
Here’s a guide on minimum Boveda and size:
Boveda 4 gram: 7-14 grams of medicine.
Boveda 8 gram: 14-28 grams of medicine.
Boveda 60 gram: 112-450 grams of medicine.
Boveda 320 gram: up to 5 pounds of medicine.