Timing for change of visa status

I came to Japan as a dependent and changed to a work visa that’s tied to my sponsor.

As they will not sponsor my visa extension, I want to apply for change of residency status back to being a dependent before my contract with them (temporary work contract) expire by end of January. They are aware that my contract with them will be cut short if my dependent visa is granted earlier than the contract’s end.

Having the change of visa granted in the first 2 weeks of January will be ideal for me as I don’t want to overstay in case it is not granted, but hopefully still able to work by end of December.

I just want to know though:

1. When changing my status of residency, is there also a 2-month extension for those who applied? Or is this only for those who applied for an extension of their current status?

2. If I receive a postcard from immigration in December, and if it looks like I have been granted the change of status, can I return on January so that my status will only change by then? How long can I hold unto the postcard once it arrives?

3. I remember there is a page for the average processing time for visa processes. Does anyone have a link to it?

Any other advise is greatly appreciated.