D4 Starting issue

Evening all.
I have put my 2012 D4 on the road this week, its the first Discovery i have ever had any thing to do with so this may be me at fault.
Press the button once and the ignition comes on, press it again along with brake peddle and the engine starts, mine doesn't always start straight away, there is a delay before it makes any attempt to crank, another time it cranks straight away.
The owners book says press and hold the button and brake peddle until it starts.
I was always told to let a vehicle do its checks before making it crank, the book also claims some D4s have a 12 second delay before cranking. Why would it delay for that long?
Searching the internet, it claims press once for ignition, then brake peddle, then press and release the button to crank / start.
This morning i pressed the button for ignition, then again for start, cursed and swore at it and it started by itself.
So which one is correct if any, is it me doing it wrong or is there a fault with the car and why on earth would some D4s have the 12 second start delay

Press and hold the brake, press and release the start button, the engine won't crank until the glow plugs have done their thing.
12 seconds sounds excessive

Cheers.
The 12 second info come from the owners handbook, you would like the book to be correct but that does sound suspect.

Plus 1 , indeed from the owners manual, also assumed it had that delay for the glow plugs and system check to be performed

funny enough on my D3 after it’s done it’s checks and glow plug light goes out it will start within 2 x seconds

STARTING A DIESEL ENGINE

Diesel engine models may have an additional delay of up to 12 seconds between the START/STOP button being pressed and the engine starting. During this delay period, keep the brake pedal depressed and do not press the START/STOP button a second time. Doing so will cancel the starting procedure.

Note: In very cold conditions it is normal for the engine cranking time to be increased.