At pokerrooms where no US-players are allowed....when the
wsop plays.
Many,many good players will be in Vegas.
Not it's gonna change much, but every little bit helps.
About the time of the day....make sure you choose a time to play when you feel the best/fittest yourself AND when there's the biggest number of recreational players.
At Stars for example you can see how many players are logged in.
Now, if you see that number increase drastically , for example during European evening, you know a lot of people jump in, who just got home from work, had dinner and want to play some poker.
Pretty often those are not the strongest players.