Sitting around waiting for something sucks in spiral, and personally I wouldn't wait more then 2 minutes for someone who said "brb" or "afk". Waiting for lockdown matches isn't as bad, but sometimes it still takes 3 or 4 delays, during which there's not much you can start without being interrupted. I thought some small minigames/timewasters would be cool. The foremost one i could think of would be a sliding block puzzle, where you must move blocks one space at a time to resemble an image.

It would be accessible under the social panel and would have priority over other windows, meaning it would always be on top when opened.
There would be 3 different levels of difficulty, 4x4 5x5 and 7x7. Each difficulty would have its own images, 4x4 would be t1 monsters or weapons, etc. 7x7 would be t3 monsters etc.
Any progress made would be automatically kept when the window's closed,so there's no worry if a party member returned and triggered some enemies, you can just close it and work on it another time when you're bored.
On completion a small effect would appear, similar to when you complete a mission. You would also be rewarded a low leveled material related to the puzzle image (ie: a wolver would reward a beast fang, a kat would reward an owilite feather or a similar material drop)

At first you would start off with only 4x4 puzzles, but as you complete them, you would slowly unlock 5x5s and 7x7s. When you finish a puzzle you will randomly be given a new one, that you may or may not have finished before. You could also choose a puzzle that you have previously done, but at a forfeit of the material and a small cr cost. This also add the possibility for special puzzles (such as bosses) which could cost CE or cr to buy and would become available at random when you finish a puzzle, or you could select it, again forfeiting the mats.

Having something like this would definitely keep me occupied while waiting for someone to return, or a similar situation, even without the prizes.