One Day of Peace is a Card that actually helps Six Samurai under very odd builds
I don’t think it should be used in the speed related builds of it. It has application is the control designs. However the true style should be the reduction of an oppositions’ resources through speed and power for victory. 
This card is broken under many decks that only want to operate on FTK and OTK. If Six Samurai are built in a very specific way this can be achieved. For instance: A full “Red Blue” engine could make use of it.
If you have “Gateway of the Six" and two more cards card that store Bushido Counters on your side of the field you can make an infinite destruction loop with this card and "Legendary Six Samurai - Shinai”. You can skip the first three steps of the loop if you have two “Mizuho” and a “Shinai” in your hand.
Normal summon “Legendary Six Samurai - Mizuho”.
Remove counters from “Gateway” to add “Legendary Six Samurai - Shinai” to your hand and Special Summon it.
Add another “Legendary Six Samurai - Mizuho” with “Gateway” and Special Summon it.
Activate “Mizuho’s” effect by tributing the second one, and then add it from Graveyard to your hand with “Gateway”, Special Summon it, then use its effect to tribute the first one. By doing that again and again, you can destroy all cards your opponent controls.
You can then convert the loop into the following one, gaining Bushido Counters until you can OTK.
Much like the above loop, you can also create an infinite Bushido Counter loop with “Gateway of the Six”, two more cards that store Bushido Counters, “Mizuho”, and “Shinai”.
Follow steps 1-3 in the above guide, Special Summoning 2 “Mizuho” and 1 “Shinai”.
Use the first “Mizuho’s” effect, tributing “Shinai” to destroy the 2nd “Mizuho”.
Activate “Shinai’s” effect, returning “Mizuho” to your hand.
Use Gateway to return “Shinai” to your hand, then Special Summon the two monsters.
Repeat the process, using the newly-Special Summoned “Mizuho’s” effect to destroy the other. You will gain 4 extra counters on each cycle, which you can use to boost a “Six Samurai’s” ATK to create an OTK (Especially after using the destruction loop to clear your opponent’s field).

With this type of advantage A player can make use of a second turn start to a massive advantage. The idea is to draw into Gateway of the Six safely and quickly. The deck thinning tech is of various things: ”Shien’s Smoke Signal”, “Shien’s Dojo" "Reinforcement of the Army"  "Six Samurai United" "Upstart Goblin" ,Etcetera.
The small hand advantage generated by “One Day of Peace” is basically the same to the life point advantage generated by “Upstart Goblin”. It isn’t a very fast process I admit. But, with skill and the right cards I really think it could be powerful for it.

One Day of Peace is a Card that actually helps Six Samurai under very odd builds

I don’t think it should be used in the speed related builds of it. It has application is the control designs. However the true style should be the reduction of an oppositions’ resources through speed and power for victory. 

This card is broken under many decks that only want to operate on FTK and OTK. If Six Samurai are built in a very specific way this can be achieved. For instance: A full “Red Blue” engine could make use of it.

If you have “Gateway of the Six" and two more cards card that store Bushido Counters on your side of the field you can make an infinite destruction loop with this card and "Legendary Six Samurai - Shinai”. You can skip the first three steps of the loop if you have two “Mizuho” and a “Shinai” in your hand.

  • Normal summon “Legendary Six Samurai - Mizuho”.
  • Remove counters from “Gateway” to add “Legendary Six Samurai - Shinai” to your hand and Special Summon it.
  • Add another “Legendary Six Samurai - Mizuho” with “Gateway” and Special Summon it.
  • Activate “Mizuho’s” effect by tributing the second one, and then add it from Graveyard to your hand with “Gateway”, Special Summon it, then use its effect to tribute the first one. By doing that again and again, you can destroy all cards your opponent controls.

You can then convert the loop into the following one, gaining Bushido Counters until you can OTK.

  • Much like the above loop, you can also create an infinite Bushido Counter loop with “Gateway of the Six”, two more cards that store Bushido Counters, “Mizuho”, and “Shinai”.
    • Follow steps 1-3 in the above guide, Special Summoning 2 “Mizuho” and 1 “Shinai”.
    • Use the first “Mizuho’s” effect, tributing “Shinai” to destroy the 2nd “Mizuho”.
    • Activate “Shinai’s” effect, returning “Mizuho” to your hand.
    • Use Gateway to return “Shinai” to your hand, then Special Summon the two monsters.
    • Repeat the process, using the newly-Special Summoned “Mizuho’s” effect to destroy the other. You will gain 4 extra counters on each cycle, which you can use to boost a “Six Samurai’s” ATK to create an OTK (Especially after using the destruction loop to clear your opponent’s field).

With this type of advantage A player can make use of a second turn start to a massive advantage. The idea is to draw into Gateway of the Six safely and quickly. The deck thinning tech is of various things: ”Shien’s Smoke Signal”, “Shien’s Dojo" "Reinforcement of the Army"  "Six Samurai United" "Upstart Goblin" ,Etcetera.

The small hand advantage generated by “One Day of Peace” is basically the same to the life point advantage generated by “Upstart Goblin”. It isn’t a very fast process I admit. But, with skill and the right cards I really think it could be powerful for it.