Nothingness: Take a 3-day bank and do the same math you did with the 10-day bank. I guarantee you will arrive at the same results. It's actually the bonus what the key is. The bonus tells you the average speed with which you need to move without timing out. With both 3-day and 10-day bank, you need to move, on average, 1 move per day (if the bonus is 1 day), so the total length of the game will stay the same.