I run two local physical servers, one production and one dev (and a third prod2 kept in case of a prod1 failure), and two remote production/backup servers all running Proxmox, and two VPSs. Most apps are dockerised inside LXC containers (on Proxmox) or just docker on Ubuntu (VPSs). Each of the three locations runs a Synology NAS in addition to the server.

Backups run automatically, and I manually run apt updates on everything each weekend with a single ansible playbook. Every host runs a little golang program that exposes the memory and disk use percent as a JSON endpoint, and I use two instances of Uptime Kuma (one local, and one on fly.io) to monitor all of those with keywords.

So -

• weekly: 10 minutes to run the update playbook, and I usually ssh into the VPS's, have a look at the Fail2Ban stats and reboot them if needed. I also look at each of the Proxmox GUIs to check the backs have been working as expected.
• Monthly: stop the local prod machine and switch to the prod2 machine (from backups) for a few days. Probably 30 minutes each way, most of it waiting for backups.
• From time to time (if I hear of a security update), but generally every three months: Look through my container versions and see if I want to update them. They're on docker compose so the steps are just backup the LXC, docker down, pull, up - probs 5 minutes per container.
• Yearly: consider if I need to do operating systems - eg to Proxmox 8, or a new Debian or Ubuntu LTS
• Yearly: visit the remotes and have a proper check/clean up/updates