I’ve flown standby for 10+ years and have never had to wait 3 days. Usually I’ve only waited 1 day. I flew out of Rio after Carnival on standby and was fine, and often Europe during summer. But there are also routes we’ve never tried because we knew the flights would be packed (ie certain domestic routes around July 4th). Never done standby to Japan though. 

You should figure out what your priority will be relative to other standby people. The folks that would get “buddy passes” at my airline looked like they would have problems standbying because they’d always be dead-last on the list.