Think about it. A 240x320 TFT like ILI9341 has got 76800 pixels (153600 bytes of memory).
You can draw all 76800 pixels from an external RAM quite fast e.g. in 50ms.
Do you have external DRAM or SRAM?
But you want to switch "instantly".
This is only possible if you have a smaller screen e.g. a 128x128 panel with a 240x320 controller.
Or you accept less colours.
SSD1963 is the only controller that is sometimes mounted on smaller panels than 800x480.
Most controllers can do 256 colours instead of 65536 colours.
David.