I do really agree that it is not the best idea to trade on Monday and Friday, but speaking of trading hours, I am quite skeptical about it. If we talk about trading forex, this market is extremely dependable on what is happening in the world. So, the funniest thing is the fact that there are always some events happening. That is why, I do understand that you mentioned the time of the highest volatility, but it can every minute really, so you should be prepared to it. As for mondays and fridays, I still trade in the evenings of mondays and mornings of fridays. I know that these days are full of events which are hard to predict, but I feel upset when I don't trade for all day long. It just looks like the waste of opportunities to earn the profits.
Smallcaps Thur-Friday are usually bad. Halfdays just before a long holiday In the options market, Friday can be a big hit or miss on the day of expiry. OTM calls are insanely risky. Some of my biggest losses came on a Friday. However, I've seen some big moves in AMZN, TSLA, etc. for largest one day % gains during fridays since premiums are at their lowest for that week. Just never had much luck in capturing them.