In the end I’ve decided to retain an overnight charge window that sits within cheap rate window (mine is Ecotricty so is either midnight to 5am or 1am to 6am depending on whether it is winter or summer so I have set it from 1am to 5am) and then rely on the RFID tags, which I’ve registered and which work. I want the overnight schedule if I just leave the car plugged in and can use the tags to override if I want more.
I struggled to register my ID tags but succeeded following help from @daveb01 link to post here - following his instructions precisely (as clarified by my questions) worked for me: RFID tags not working