Just checking to see if you have visited the links I’ve provided?
You may find some answers that maybe useful for you.
To represents the months, you’d need 12 different images. Same as the rooms, you’d need 31 images. If you are using a Car image, it may get confusing if you have more than a few appointment.
I think it maybe better to just use the area of the actual place you have an appointment at.
So if you had an appointment at the Dentist, simply place an image that would remind you of the Dentist. Perhaps an image of a “Tooth”, or even the treatment room itself.
Here I have an example of how I use this Mnemonic clock that covers the area with the meeting times. Hope you find it useful, ot it may give you some more ideas;