Consider the situation:
I want to attack a player who is 1 hr away from me. My fire feast will last for 30 mins only. To get the effects of fire feast do i need to start it when i send the attack or after my troops have reached half of their journey (i.e. 30 mins remaining for the attack to happen)?
Also let me know if i have started the lightning feast when i sent an attack but it was over before the attack was done, so in the return trip will my troops have normal speed or double?