How can I set up a recurring automatic reply during specific hours?

I work in an industry where my clients may require urgent assistance outside of normal business hours. My business engages a third party to handle after-hours emergencies on behalf of the team, but we often receive complaints that clients cannot easily access the after-hours emergency contact number, despite it being available on our website and our after-hours voicemail. In most cases, clients will call the team and disregard the voicemail, then follow up with an email complaining that we're unavailable.

It would be beneficial to have the option to set up an automatic reply where the after-hours contact information is sent to clients when our staff are emailed between 5pm and 8:30am, 5 days per week.

I have tried using the rules feature and fiddled around with the automatic reply feature, but neither would allow me to set up a recurring automatic reply without setting a start and finish date/time. I also checked whether it's possible to synchronize an automatic reply with my calendar block-outs, but this wasn't possible either.

Any guidance would be appreciated.