Idk if I miss read something but I thought 50% was supposed to last the full 30mins. Yet mine ended saying, "You have used up your exp for the day" I had 18mins left. I'll take a screen shot next time if its not supposed to do that.
did you use it from (eg) 11:48pm onward on day 1, therefore using 18 minutes of it on day 2, then log in again within day 2 and use the 12 mins from day 1?