For me it is not directly dependent on the number of hands but on the ability to concentrate. If I'm willing to mentally torture myself and play my A game, it's not a problem. However, this ability decreases over time depending on my personal state of mind.
Therefore, I try to set myself a certain realistic target time before the session, which I ideally stick to. Of course, I don't always succeed, because other influencing factors are at work, but for me it's better than grinding without a time target.