To my opinion the Ninja Tower event is too time intensive. You have to play (at least…) ten battles per day on five consecutive days. And this is on top of all the other game activities since it does not consume WE.
I suggest to spread it over a longer duration. Instead of getting 10 tickets per day over 5 days, for example, get 2 tickets per day over 25 days. In case there is an issue with having the Ninja Portal open all this time then open it, for example, only over the last five days of the event.
Thanks for reading,