hello. i think it may be a good idea to increase duration by like 5~20 seconds. some may argue 20seconds to be a bit too long. but 5~15 seconds could surely be acceptable.

why? well with the way it is you can't keep Huton up 100% of the time AND execute two other ninjutsu in-between. it takes roughly 1.5 seconds to execute your ninjutsu. so at the end there is at least 3 seconds of Huton down time.

3 seconds not so bad. but that's only if you are executing ninjutsu ASAP. other-wise the player may feel inclined to skip some ninjutsu in order to refresh Huton at an opportune moment. and then if they should so happen to change their mind, the remaining duration of Huton just might make them change their mind again.