I have almost the same setup and for the same reasons. I struggled with settings until I bought Solar Assistant on the Raspberry PI. What i did was automate the charge from grid during midnight and 7am then automated switching off charging until midnight again. You can change all of the settings via Solar Assistant and I changed the priority to battery then utility for most of the time. The great thing is that you can monitor everything through a web page locally. I started with a socket timer like you but this way you can leave the inverter plugged into the AC always and just automate the charge mode changes. This way if my battery ran out at 10pm there was no interruption because the AC was still plugged in. Just set it and forget it. I had to create my own cable following a youtube video I found and had to buy a cable and rj45 crimper but it was flawless after connection.
