[soulfuldog]

https://www.amazon.co.uk/gp/help/cus...deId=201734090

According to this its pretty much 40 seconds to do a restart on all and so there's not a short or long hold difference.

To restart your Kindle Paperwhite (5th Generation), and any Kindle e-reader model 6th generation or newer:

• Press and hold the Power button for seven seconds until the Power dialog box appears.

• Tap Restart.

• Note: If the Power dialog box doesn't appear, press and hold the power button for a full 40 seconds to restart your Kindle.

To restart Kindle Touch (4th Generation), and Kindle (5th Generation):

• Press and hold the Power button for a full 40 seconds. After the first 6 to 8 seconds, the screen will go blank, which is normal. Continue holding the Power button.

• After 40 seconds, release the Power button.
  The charge indicator light will turn on after a few seconds.