Then you should try to pick a time that you are awake and able to take it every day. If you don't take it at around the same time every day, it won't be as effective. Now, if you pick 6pm, for example, and one day you take it at 6:12pm, no big deal. Differences that small aren't going to matter. However, when you're talking about being hours late, that's when it can mean trouble.