I'm glad you asked this question as it's an important idea to cover. Considering that the primary difficulty for most students with regard to LG is time, making sure that we start at the appropriate answer choice for questions when we can is going to help greatly.
In this case, the question is asking for the latest that J could be placed. Immediately, we should be trying to push J into the latest possible slot, as opposed to working from the earliest onward.
Given the interactions between the rules, we know that J comes before three other variables (G, I, and M). Immediately, we know that J cannot be in the last 3 slots because a rule violation would ensue as at least one of G, I, or M would be knocked off the diagram.
In the video, this resulted in us testing 1965 first because it is the latest slot that would not result in an obvious conflict. After ensuring that this hypothetical works, then we can confidently select that answer choice.
But now consider the flip side, had we tested starting from A to E, then we would need to test all answer choices to show that 1965 is the latest possible start. Using deductions such as J cannot be in the last 3 slots helps us choose the correct starting point.
I hope this helped. Please let me know if you have any other questions!