Few blackjack players really keep track of how fast the games are going when they're playing. Sure many smart players try to monitor the amount of time they're spending on the blackjack tables, but this isn't the same as keeping an eye on how many hands are being dealt per hour. 

In any case, it's important that you pay attention to how many hands are being dealt each hour. The reason why is because casinos carry a long-term house edge over blackjack players, and more hands means you are being exposed to this house edge longer.

Now the counter argument to this fact has always been people asking why you'd want to play less hands when the point of blackjack is to try and make money. But while this may be true, the reality for the average player is that their chances of making profits decrease when more hands are dealt.

You especially need to be aware of this when playing online blackjack because the software deals hands at rapid speed. If you were determined enough, you could play hundreds of blackjack hands per hour since there is little wait in between when you're finished playing a hand, and when the next one is dealt. 

This being said, it's important that you pace yourself when playing online blackjack games. If you have to, do other things in between each hand such as folding laundry or cooking so that you're not so tempted to play hands in quick succession. Or you could always play 10 or 15-minute sessions because you're basically playing the same amount of hands as somebody would get with an hour's worth of play at land-based casinos. Whatever you do though, just make sure that you're not playing tons of hands in each online blackjack session.