Peaceful Mode is a mode of Google Snake Game in which you cannot die. The game ends when you collect 252 fruits. In this game mode, you can also pass through the outer border. Instead of dying, you are transferred to the other side of the board.
Unlike all other game modes, in Peaceful mode you can't die.
The board is 15x17, this means the worst case apple is max 16 blocks away, where you have to run half the board for "up-down" as well as "left-right". Imagine as if you are in the middle at all times, the shortest path to any apple will be 16 blocks (max) or less.
16 blocks take around 2.435 seconds.
As for how apples spawn, they can only spawn where the snake isn't filling up the block. They spawn 100% random, as confirmed by the developer. In peaceful however there's something extra, when you reach high numbers, for some reason, apples tend to spawn less in the right side of the board - looking at all the 252 runs you can see this happen across all of them. Where even if there's 2-4 empty columns in the right ready for an apple to spawn there after you eat one, it never does. the dev says that apple spawning logic in all modes is uniformly random - so this may be a bug.
Update: turns out this was a bug, and it's now fixed, as the devl said: "The logic for finding an unoccupied cell for the new apple wasn't taking Pacifist into account and was assuming that the snake was occupying a unique cell for each of it's body segments"
Regardless, the optimal strategy for any Peaceful category of apples is to aim for the shortest path to any new apple.
Another helpful tip is after you eat an apple, if possible, go for an empty space where another one might spawn. When you are about to go over yourself - that's a block where an apple won't spawn and going over it will cost time, this is especially helpful in high apple categories, as empty blocks become less available, aiming for them preemptively will save time.
Peaceful mode was added to the game on January 19th, 2020.
All dates in UTC
20th January 2020: 35.55 seconds by Aegwynn
21st January 2020: 34.94 seconds by Eliot_Mk1
22nd January 2020: 33.22 seconds by Yarmiplay
24th January 2020: 32.11 seconds by diggitydingdong
24th January 2020: 31.86 seconds by Yarmiplay
8th March 2020: 31.74 seconds by SpaceDoge
13th March 2020: 31.50 seconds by Yarmiplay
19th March 2020: 31.367 seconds by SpaceDoge
23rd March 2020: 31.00 seconds by Yarmiplay
3rd April 2020: 29.89 seconds by Yarmiplay
16th May 2020: 29.15 seconds by Yarmiplay
3rd June 2020: 28.65 seconds by Yarmiplay (unverified)
3rd June 2020: 28.55 seconds by SpaceDoge
3rd June 2020: 27.26 seconds by Yarmiplay
20th January 2020: 1 minute 21.57 seconds by ATCRyan
21st January 2020: 1 minute 18.90 seconds by Aoten7759
22nd January 2020: 1 minute 07.32 seconds by Yarmiplay
20th March 2020: 1 minute 06.87 seconds by Yarmiplay
15th May 2020: 1 minute 03.141 seconds by SpaceDoge
3rd June 2020: 1 minute 01.54 seconds by Yarmiplay
4th June 2020: 59.01 seconds by Yarmiplay
20th January 2020: 2 minute 43.60 seconds by ATCRyan
21st January 2020: 2 minute 38.133 seconds by Aoten7759
22nd January 2020: 2 minute 35.62 seconds by Yarmiplay
23rd January 2020: 2 minute 32.27 seconds by Yarmiplay
25th January 2020: 2 minute 29.76 seconds by Yarmiplay
8th February 2020: 2 minute 28.81 seconds by Yarmiplay
29th February 2020: 2 minute 27.65 seconds by Yarmiplay
12th March 2020: 2 minute 23.93 seconds by Yarmiplay
13th March 2020: 2 minute 20.93 seconds by Yarmiplay
20th March 2020: 2 minute 16.65 seconds by Yarmiplay
21st March 2020: 2 minute 13.45 seconds by Yarmiplay
3rd June 2020: 2 minute 11.37 seconds by Yarmiplay
20th January 2020: 6 minute 53.50 seconds by ATCRyan
21st January 2020: 6 minute 39.916 seconds by Aoten7759
22nd January 2020: 6 minute 33.93 seconds by Yarmiplay
25th January 2020: 6 minute 14.98 seconds by Yarmiplay
27th February 2020: 6 minute 07.88 seconds by Yarmiplay
20th March 2020: 5 minute 56.16 seconds by Yarmiplay
16th May 2020: 5 minute 54.37 seconds by Yarmiplay
3rd June 2020: 5 minute 40.36 seconds by Yarmiplay