About an 8 hour flight. Try to fly on a Mon/Tues/Wed during late Sept, Oct, early Nov, late April, early May, when plane loads are light, then it’s possible to have a row all to yourself. Do not go late in May else you’ll get caught in things like UH graduation, Ironman events, WalkAThins. Load up your phone or tablet with Kindle books or movies.
I agree with everything BiglyCommentary said.
Also, get to the gate early, at least an hour before boarding. Southwest does not have assigned seats and boards passengers in groups based on when you get there. You want to be in the first group. Before the first group boards they board passengers with disabilities or small children, so many seats will be taken before the first group boards. It is even worse if you are not the plane’s first stop to the destination, since the best seats will already be taken before the plane arrives at your stop.