The phrase "arbitrary deadline" means a deadline that is chosen randomly or without sufficient reason, rather than being based on a logical or necessary timeline. Full definition
Credit card issuers are no longer able to set early morning or other arbitrary deadlines for payments. (creditcards.com)
It takes them forever to make these GT games, and they often cut corners to meet arbitrary deadlines. (n4g.com)
Unfortunately, they provided limited information and made threats under arbitrary deadlines which were not reasonable under the circumstances. (businessinsider.com)