I think that there is no correct time, I think it is more than having enough time to be able to play as calmly as possible, when you enter a tournament and have things to do, you do not play well because you know that you have other responsibilities and that will makes it fail. If you put me to choose a schedule, it would be early in the morning but after having rested very well, the mind is fresh and you hardly make any novice mistakes while playing, apart from your mind being less distracted and more concentrated.