How do you set a countdown timer to attack a target in Eden so the rest of my guild can see it?

On the guild marker menu, under the section where you write a description, there is two options. The first is to set a timer, enter the game time hour of the attack in the timer section. For example if you are attacking at +8 you would put 08:00:00 in the timer. You can only set timers at reset on the day you will battle. Therefore you cannot set timers for Reset battles. The second option is to give a 3 minute reminder to guild members via a push notification on their phone.