It is all about your preference theoretically, it is best to be consistent about when you get in there so your body can be accustomed to going that specific time and be mentally prepared at that time. Some people like to go late, some really early. I personally think that the more meals you can get in that day after your WO, the better so earlier is provbably best in that aspect. your test levels are highest early in the morning too. It really is just personal preference though