They're trying to get better stats on their starter, which will allow it to OHKO more things and therefore end those battles faster, and/or get a favorable result as far as running through grass without getting ambushed by wild Pokemon when it's still too early in the game to buy Repels.
Their study of the game in pursuit of better times has gone as far as deconstructing the order in which the game spits out "random" numbers for whatever purpose is necessary, and while it's not legal to have a memory probe active that can give you feedback outside what you would normally get from watching the screen (such as telling you when the game is about to give you "good" numbers), with enough practice it can be distilled down to "Wait a specific amount of time, then start the game."
