Adjustable delay time for power on - problem with relay and a flash at power on

[DieNummerEins]

Is your feature request related to a problem? Please describe.

My setup:

• 1 ESP32 WLED controller (always on with its own PSU)
• 10 meters SK6812 rgbww led strip
• 6 PSUs every 2-2,5 meters as power injection on 230V line
• relay (SSR) => inrush current limiter in front of 230V line (as protection for fuse not to blow out, what it definitely does by more than 3 PSUs)
• relay is connected to WLED to power off/on the PSUs

My problem:
If I turn lights on (e.g. "turn on" button in GUI) I see first a short flash with random colors. It seems as the PSU needs a bit of a second to provide stable 5V but WLED already forces the LED to light up.

Describe the solution you'd like
Like in issue 812 (see below) a "delay on power on event" would help. If I click on "power on" (via GUI) or "power on" command is send, WLED first actuate the relay and only after a time to be set (delay time) forces the LED to lighten up.

Describe alternatives you've considered

I tried a workaround via a playlist (first a black preset for 0,2s duration, then the desired light configuration). It works fine, but this has disadvantages like described in
#346
And, I think, I cannot turn light on with this playlist vie GUI (turn on is just turn on without playlist/preset)

In a thread I cannot find right now there were a solution considered to make "turn on/off" event more generally. I mean turn off via GUI and the same turn off on boot. On boot I can start a playlist/preset, but not with GUI-turn-on-button. This feature would make a small difference at the playlist/preset-workaround for my entire problem. I plan to have 30-40 WLED inside/outside my house, not to turn on/off via GUI isn't nice. With the feature to customize the turn on/off event (not just at boot), I can hide my problem from using experience, it is still a workaround (based on the missing delay option) but it is more user friendly. I will submit this as a separate feature request.

Additional context
I commented a similar thread:
#812

...and explained the situation in discord issues channel on October 5th/6th 2023

[blazoncek]

My recommendation is to use Multi relay usermod and connect relay switch to a LED GPIO output.
This will achieve desired result without changing code at the expense of additional relay (or some other switch).
Multi relay usermod has adjustable on delay.

[softhack007]

• boot-up delay to fix wifi not starting in some setups #4060

Allows to add a delay at startup before powering on LEDs and other units. Only available in custom builds by -D WLED_BOOTUPDELAY=500 (or any other delay in milliseconds)