I find late works if you are able to stay awake lol.
Late fridays and Sats - you will soon work out the familiar faces and grinders and i agree with Fundiver - table select is crucial, ive been known to ahem lets say look for certain players who are profitable to play against and you always know when they recognise you - they disappear!
Evenings and weekends: More players, more competitions, but also more distractions.
Weekday mornings: Fewer players, quieter, but often experienced opponents.
Choose according to your own concentration - ideally, play when you feel most motivated.