No I did not read every single one of the postings in the forum before posting this circuit. R3 is not redundant, since it establishes the decay slope through the 4.7uF cap so that the off-delay is set to 3 seconds.
You did not really answer my question. I would say the transition from your earlier circuit in,
https://www.eevblog.com/forum/projects/two-mosfet-soft-latching-startup-switch/to the current one is quite striking (I also do not want to try to understand why there is the need to start a new thread on the same topic).
Anyway, if you can't realize R3,C3 and C2 are redundant, you did not really understand how this circuit work.
In this case, C2 is not just redundant, it can be actually harmful. As for R3 and C3, the circuit looks more like a bad copy of the
UT61E mod I did (
https://www.eevblog.com/forum/chat/ut61e-auto-power-off-modification/
).
I have there two RC timing circuits (one of them is like your R3 C3) for good reason since I have two power off ctrl signals to handle: one is from manual button press the other is from APO.
The APO signal should do power off ASAP, hence it uses the short time RC. On the other hand, The manual power off needs to have a (3sec) delay since it shares an existing button that short presses are already assigned for the meter use, hence it uses the longer time RC (your R3C3). Also due to the shared nature of the button, one leg of the switch must be on ground.
Now in your case, the longer time RC becomes redundant since you deals only one power off signal. Adjusting C1 is enough to change delay time.
This is clearly a simple circuit, so of course it is not going to be "new".
Well, this is not entirely true. The self-latching part is a common knowledge. But, as for this particular power on/off mechanism, I designed it from fresh (for a particular use). If someone else did it already, I would like to be enlightened. And I can still claim I independently designed it.