I'm actually surprised by all of the comments. The community jumped right into solving OP's problem and has largely ignored the OP's original question of "how could I begin investigating this?" Another variation of this question could be "how do I troubleshoot complex network issues?"
After 20 years of network/system/software engineering across a wide variety of network sizes and levels of complexity, I teach people the following method to troubleshoot complex network issues:
1. Write down the symptoms that you're seeing. How do you know something is wrong? What do you see happening?
2. Draw a diagram that includes all of the components and nodes involved. (this is hard)
3. Develop some hypotheses that could be worth testing. (this is hard and highly variable based on knowledge/experience)
4. Establish a "test plan" that allows you to prove/disprove the hypotheses while making minimal changes to the system. Start from one source device and work your way out to the farthest component you identified in your diagram. Start at the lowest OSI layer and work your way up.
5. Methodically test components, step by step, along the diagram.
6. As you test, record your results. Add new hypothesis to the list as you gather more information but don't start testing them right away! You can develop a new test plan after you finish the first one that proves/disproves your new hypotheses.
7. Repeat all steps, adding new information, until you find a solution.
I know this seems like a lot of steps when you're just troubleshooting a WiFi issue at home--it may be overkill. However, this framework applies to that scenario or when you're diagnosing any complex network issue. You'll learn more about the systems, protocols, and devices that truly make up the Internet than you could ever imagine. Through repetition and experience, these steps will get easier and some of them can happen quickly and in your head.
To help you get started, here's some info for steps 1, 2, and 3:
1. From your post: "3:40pm every day my wifi loses internet access. My devices remain connected to the network, but all traffic dies. Almost exactly 1 minute later everything is resumed"
2. Start your diagram off as an "equipment string diagram". This will include all physical devices between you and the Internet. Along the way, you may need to modify the equipment string diagram to include "virtual" devices, network segments, various protocols/servers, etc. Your diagram should include at least the following items:
- Your laptop/desktop. If it's happening to all devices, then pick one. Identify your IP and MAC addresses
- The WiFi access point that device is connected to. Identify the IP and MAC addresses
- Any switches, firewalls, modems, etc that connect from your WiFi access point to your Internet Service Provider (ISP) and their IP and MAC addresses.
- The "next hop" from your modem into the ISP's network. You can use a cloud to represent the ISP's network that you don't know/understand, but always identify the IP address of the device that your modem first reaches. If you can find the MAC address (or other OSI Layer 2 address) as well, even better.
That's the equipment string between you and "The Internet". For now, you can ignore the complexity inside the ISP's network and beyond. You might have to add more of that later, but start small.
We know there are other components involved in making the Internet work that introduce complexity and can cause issues along the way. Let's list them on your diagram and identify what servers are used and where they might be located.
- DHCP (local to your network and also between your modem and ISP)
- DNS (could be local to your network and often is a third party service either run by your ISP or not)
- Encryption (VPNs, SSL certificates, network device clock settings, etc)
- IP routing (what devices do IP routing? Hint: all devices that operate at Layer 3, using IP, do IP routing--including your workstations)
3. Some hypotheses (some were identified in the comments):
- Is there a device in the equipment string that is rebooting every day?
- Is DNS intermittently failing?
- Is DHCP releasing/renewing your IP address assignment? This could be from your device -> local DHCP server OR your modem -> ISP DHCP server
- Is there an upstream connectivity issue with your ISP?
- Is your WiFi access point losing connectivity?