Hi there!
I'm from Barcelona and it's 10:47 PM here (GMT +2)
In addition to all of this, and related to the "activity periods", I use a tool called World Time Buddy to keep an eye into different timezones: http://www.worldtimebuddy.com/
I like to schedule my comics with three timezones in mind: GMT +2 (that's my tz and some kind of "standard Europe time" that works for me), GMT -7 (for all the US west coast) and GMT -4 (east coast).
Also, I always set my comic strips to be published at 6 PM GMT +2 (9 AM in GMT -7 and 12 PM in GMT -4). The general idea is to avoid "weird"/non-practical hours (If this kind of thing can exist, of course : P), but this requires to know your readers and their behaviour (for example, my spanish comic is scheduled at 8 AM 'cause lots of my readers works in offices and open my website when they arrive at their workplaces in the morning) so maybe I'll need to change or adjust this time in the future...