Depends what I'm flying, where, and why.
Let's say I was doing a test in a Piper Arrow - it has a really thorough manual, and I want to be withing 30 seconds or so on target. I'll use all the numbers in the manual, and spend considerable time on it.
Let's say I want to fly 200 miles for the day in my own aeroplane. I'll use a standard speed, revise my plan en-route, and not worry about being 5-10 minutes out at the other end.
Where you are on the map is important, being a bit out on times, really isn't - so long as you use instruments or map features to keep the first right, don't worry about being a bit out.
Unless you are taking a test, or flying farepaying passengers with strict timelines.
G