Zelda II: The Adventure of Link/Luck Manipulation
From Red Candle
The Zelda II RNG changes with every frame. In the NES version, the counter starts when SDA timing starts. Generally that doesn't matter, since things will never happen at the same time, but the one key exception is that in any category where the North Palace Magic Container is done first, a 50 point bag can be manipulated.
Here is a chart of the Zelda II RNG at the start of the game, with a 10 frame moving average. Each bar represents the numbered frame, and the 9 frames preceding.
For the P Bag drop, the two key windows are the ones at about 1600 frames, and at about 1920 frames. Hit either of those windows reliably, and P Bag drops go from the usual 1/8 chance, to much higher.