I'd say unimportant as long as you're willing to SKA them. Sathanas and Belphegor are multistage fights by default, but can be made single-stage.
I'd prefer to not have to, I'm only on day 72 though, so there's plenty of time for me to say, try to sweep up both in the 90s or so.
The only time I release the collar is on day 3 for the hydrangeas so I can pink scene the alchemist, Charlotte's release, and +3 attack.
If I may ask another question, is it possible to still claim the bandit leaders bounty from the union-lumerian bridge crossing if you gave him a blowy to get through? Bit of a completionist, but if it was a one or the other option, no big deal.