Diana here from the Shopify Support Team.
If your clients want to stop people from buying rather than browsing, you will definitely need to get creative with some customized code to either reduce the stock during closed hours (or perhaps hide the Add-to-Cart button), as I too have had no luck in the App Store when looking for a simple way to automate this function.
However, if your clients want to stop people from accessing their site entirely between the hours of 7PM and 7AM, consider altering their password.liquid page into an 'Hours of Operation' page. Since Shopify has an 'Opening Soon'/'Closed for Maintenance' type of password page built directly into the system (which can be easily toggled from right in the Admin with one click), your clients would just need to go to Sales Channels > Online Store > Preferences, and click the 'Password protect your storefront' box to lock out everyone from their site when they want to stop accepting orders, and then again when they want to reopen the ordering service again the next morning. This requires a tiny bit of manual effort on the part of your clients, so it may not entirely be what you're looking for, but consider it as an alternative.
I hope this helps a bit, and good luck with the store!
My first thought would be disabling the checkout button on the cart page with a helpful message when the store is closed. Reducing and increasing the inventory every day seems like it could be error-prone.
If you need some more help, you can send me an email to thejakneeumann (at) gmail (dot) com.
I am running takeaway service where we operate from 4:00pm to 10:30pm every day except we closed on Tuesday. I having problem to amend the limit Open hours, does any one have solutions for this. I have tried password enable but this is manually and have to do every time. Your help will be appreciate. Thank You
I developed an app where you can set your store hours and show a custom message for your customers when the app is closed. It also disables your add to cart and checkout buttons. Check it out: https://apps.shopify.com/were-open
The app also has a feature called "smart message" that adds the next opening hours to your custom message. Please contact me if you want me to add a specific feature.