my guess would be from 6pm till....  or when most people get back home from work/school

But during the day you get more Euro Donks.

I've found it to be particularly soft the later you play (7pm+ for me), unfortunately I don't play very late these days.
The lower stakes you talk about the less the time matters, as there are more games going on at all times the lower you play.

I'm a Euro player, but super flexible regarding play time, so I end up playing in virtually all time zones (even Aussie  time zone).
I checked out HEM, and these are my observations:
1) EU afternoon / US morning: Horrible! By far my worst results are during that time zone. It's the time when US/EU grinders play...and they're normally better than the average donkey who plays after coming home from work.
2) EU evening / US afternoon: Much better, you get the "play after work" EU donkeys. The later it gets, the better because some clearly play after coming home from the pub ;)
3) EU night / US evening: Past 1am EU time is by far the best time to play...the donkey vs good player ration isi through the roof. You'll often find the occasional Euro playing at 4am his time because he can't stop. Most of the time those guys are the worst players ever :)
4) EU early morning / US night: Great too...the later it gets for US players, the more bad US players you'll find.
In summary, I quit playing during EU afternoon time, because the competition is clearly strongest during that time.

yup, its kidna same for me - i am from europe too. I really dont have as good results in early afternoon time all the way up to 5pm or so (european time) as i have after that, not to mention playing like 3-5am is best for me. But it could also had to do with the fact, that i usually get up at 11am, and start playing when i am not completely awake..