by Bushwalker8 on Tue, 26 Mar 2019 8:36 +0000
The timing of the display is normally dependent on the head unit software & state.
The Toyota reverse camera itself is wired to be always on and sends video up to the front whenever the vehicle power is on. The transmission reverse signal also goes directly to the head unit to signal to the software when to switch to the reverse video display.
I can't check the OEM timing as I've replaced my Toyota / Fujitsu Ten head unit with an Android one but it's not unusual for head units to drop back to a standby mode for a period after turning off the vehicle.
If the vehicle is re-started again within that period (for mine it's 10 mins) the reverse camera display is almost immediate as the software remains loaded and ready to go. However if the vehicle is started after the head unit eventually completely shuts down it needs to at least partially boot up again from cold to a point where it can get the video software running and this takes a lot longer.
Same as booting your phone or a PC, it's just another device.