There are times when every little detail must be perfect down to the last pixel. Most times though that is not the case. Most times good enough is definitely good enough.
It's very easy to get caught up in the small stuff and lose sight of the bigger picture. Focus on making something perfect for half a day, but avoid the highest and most critical priorities.
Having done a little carpentry work with my father this summer, my new favorite saying is "Measure Twice. Cut Once."
It's beautiful. Clearly, you want to make sure you are allocating the proper amount of time to planning. You also have to take action though and cut. It's not measure 14 different times throughout the day and get 8 different opinions on your measurement. You measure twice, cut, and then move on. Take action and deal with whatever happens next.
Don't skip on the details. But don't get paralyzed either.