Really important point! Sitting too long without breaks is not good for your health.
For people who work on computers or spend lots of time on them at home, I recommend they download a free Timer from the Internet. These little timers can be set for as long or as short a time as you wish and will pop up or sound a notice when your selected time expires. Most often, the more strict recommendations are to get up from sitting every 15 to 20 minutes. That's too short for me so I set mine for 30 minutes then get up and do a minute or so of stretches or exercises or get a glass of water or just walk around. When I return to the computer, the first thing I do is reset my timer. This is the only way I can avoid spending multiple hours sitting without a break.