no, the speed is not relevant. You don’t have to run it 24/7, but the longer you run it, the higher the chances are.
Think of it as a lottory which happens every minute. Every minute one of 28,724,197,888 RDD (current circulating RDD according to coinmarketcap) is the winner. The more you have, the higher the chances. The chances increases with your wallet weight, which increases the longer you run the wallet.
With much luck you can even with 10 times in a row, but this makes no difference, because the logic behind makes you earn as much that you get approx. 5% a year, no matter how often you win.
As far as I understand you do not need a fast computer, but to mak chance of winning a stake you need to have your walled online. Also being a full node will increase your weight and chance to win… Although I have not have much luck yet. but just started stacking (+/-3 weeks now)