Malicious compliance from a freelancer: I set up an auto-reply and now my most chaotic client is losing his mind

Some background. I'm a freelancer, mostly work from home, occasionally rent a desk at a coworking space when I need to feel like a real person. One of my long-term clients, let's call him Derek, has this pattern where he ghosts my emails for days or sometimes entire weeks, then resurfaces with "hey need this ASAP" like time is a concept that only applies to me.

I've mentioned it twice. Nicely both times. He'd agree, apologize, and then do it again within the month.

So a few weeks ago I set up an auto-reply for his emails specifically. Nothing aggressive, just: "Thanks for reaching out. Due to current project load, responses may take 2 to 3 business days. For urgent requests please refer to section 4 of our contract regarding rush fees." Which is a real section. That I wrote. That he signed.

First week, nothing. I think he didn't notice or just assumed it was a generic reply.

Second week he sent something "urgent" on a Friday at 6pm. Got the auto-reply. Waited. I responded Tuesday morning, normal pace, professional tone. He wrote back "hey just checking you got my friday email, this was kind of time sensitive." I replied that yes I had received it and had responded within the 2 to 3 business day window as noted.

He called me instead of emailing. I let it go to voicemail and responded via email the next day.

It's been three weeks. He now sends emails that are noticeably more organised, with actual deadlines that are not "today" and context that doesn't require me to read his mind. Last tuesday he wrote "no rush on this one, end of next week is fine." I almost framed it.

I have not changed a single thing about how I work. I just started responding exactly as fast as my own policy says I will.