We need just a simple script to delete messages by regular expressions.
Also it should be after some random or desired time to protect board owners from observers (parsing endchan and searching big data on network providers in Russia by police) to make it difficult to distinguish when board owner is actually online or this is just a script.
Just it.
Copy same code from filters and modify it to delete posts at some time, but check time globally or when the board is accessed.

Just add this fields in board settings:

Anti-spam
Enable: yes no
Random time: yes no

Time to delete spam
Spam delete times: 1-4 (how much times spam should be deleted)

First time: (time of the day, if not random then every day at this time)
Second time:
Third time: