I think for analytical purposes, the time should be about an hour or more. When we spend too much time, it is a clear indication of the lack of decision power. If someone faces a problem it's better to skip trading and wait for the appropriate time later. And the more traders learn about forex trading it also depends on the more they stay ahead of the chart. I spent a lot of time trading as a beginner and I improved a lot because I spent a lot of time in front of my computer.