What is the best day of the week (weekdays and weekend) and time of day to see a wg?
You're the one paying so you decide.
If you're single, you choose any time that suits you.
If you're married, you choose a safe time to make sure you're never found out by your wife, there'll be hell to pay if she ever does.
If a WG is not available at the time you want, just choose another.
As for whether she'll be "tired" etc, that's her lookout, not yours.
You get what you pay for.
If you get a cheap East European, don't be surprised if you're treated brusquely.
Also there's no correlation between price and quality, a £120 an hour Adultwork will often turn out to be better than a £300 an hour "courtesan".