If your going to 'fix' every 6 to 8 minutes in theory you're virtually track crawling!
If however at your defined time there are no obvious landmarks to confirm your DR then what happens - this is typically where DR goes wrong. A pencil mark in the assumed position means that the next 'fix' could be quite a long way out as it may be based on erroneous previous 'fix'.
I can only claim to holding a course within 5 degrees - which means that 'fixes' have to be reasonably frequent - otherwise read above. I cannot see how 'track crawling' requires such a level of concentration, the technique is to ease 'easy' landmarks, no something obscure that happens to comes into sight at your 'fix' time. Those landmarks vary depending on where you are and what the topography is.