Purely personal, but I dislike the use of 6 minute (or any other kind of minute) marks. Why? - because circumstances may require me to change speed, altitude, or the wind correction may change.
When doing everything from the chart, I much prefer distance marks - usually 6nm or 12nm depending upon flying speed, and note time at each. That way if it took 5½ minutes since the last mark, and there are 4 marks to a waypoint, I know with little requirement for mental arithmetic that it'll take me 22 minutes to get there. Particularly useful when planning "on the hoof", diverting, or being asked by ATC to give estimates to spots en-route that you'd not worked out for.
G