The duration of the putt is how long it takes to go a certain distance, this is a skill that very few golfers ever work on and it is integral to learning how to control the speed of your putts
Grain is a very difficult concept and there is no way to perfectly categorize its effects on your putts, experience and feel for grain takes time to develop, but by using this trick to see the grain you can practice on it and analyze how it effects your ball to get a better understanding
The direction your eyes are lined up when you set up to putt is the direction your putting stroke will travel, so if you play with a hat on use the bill of the hat to make sure that your head is lined up with your target line