So, let's say if you are on your bike it takes an average of 10 seconds to encounter a Pokemon, and in HGSS, (I can test this because I'm literally playing it rn lol,) it takes 12 seconds to run away from a Pokemon if you are mashing A. (10+12)x8192 =180,224 seconds = 3003.73333 minutes = ~50.07 hours= about 2 days and 2 hours of straight shiny hunting.
This is 8192 encounters of Pokemon in general if that's not what you want I can change it.
Good luck!