If anything happens between the donation and the temporary custody, then yes. Just to be safe, at my museum we have them fill out two donation forms, a “consideration” form and then the official donation form.
If they are in a rush, then I ask them to only fill out one, sign both where their signature is required, and then I offer to mail them the copies after I duplicate what they said on the other form they didn’t write it out. This just saves writing for them.
But if they aren’t donating right then and there you definitely need to have a temporary custody form in case anything crazy happens.