Walking 8 kilometers should take you between 102 minutes (1 hour 42 minutes) and 110 minutes (1 hour 50 minutes). For most runners, a reasonable time would be about 25 minutes, or perhaps 20 minutes. A slow walker might take 40 minutes for the trip while a very fit person could do it in under 30 minutes. If you start to feel tired or out of breath during your walk, stop immediately and rest for a few minutes before continuing with more moderate efforts. Be sure to drink enough water during exercise to stay healthy. Walking is easy to do too much of; if you feel exhausted or out of breath after walking for just a few minutes, stop what you're doing and rest for several hours instead of continuing with more vigorous exercises. In conclusion, walking for health benefits is easy to do too much of; if you feel tired or out of breath after only a few minutes of walking, you've gone too far. It's important to pay attention to how you feel so that you don't end up with injuries. Walk at a rate that feels comfortable to you but make sure to keep moving to get the health benefits of the activity. Have fun!