Unfortunate change of plans, everyone As of now, I'm not going to be able to leave the event going, because I just realized scriptblock doesn't have a per-player cooldown option. Basically, I planned on making it so once you got your item, there would be some crazy, 50 year long cooldown so you couldn't get another item. The problem is, once one person activates it, the next person has to wait 50 years to get their item, and I don't think you guys want to do that. So, until I find a fix, we're going to need at least one staff member constantly manning the event, and we can't do that for an entire day like I originally planned. So instead, for now, I'm planning to run it at the original time, and maybe have another go on Friday for anyone who couldn't make Thursday. It'll be all the same fun as it was originally going to be, but the time schedule won't be as flexible.
also... my irl work schedule has me out both thurs and fri, so... Saturday night is cool to keep the event open maybe-?
Use command blocks and scoreboard. Only teleport them if they have a score of 0. Once they receive the item, add one to their score and teleport them out.