If you go to Timeanddate.com, you can get a list of Countries by Time Zone.
Your Segmentation would be fairly easy to do with
EST: Country is US, Canada AND State=X
GMT: Country is UK, etc.
Be sure to place your priority countries at the top of the Segmentation.
But when you send the email, you will need to break it up into several campaigns or a series of Send+Wait Step starting with the first time zone. Usually you can run this as the three regions:
If Time Zone Segment= EST, Send Email 1
Wait 12 Hours
If Time Zone Segment=Asia, Send Email 1
Wait 7 Hours
if Time Zone Segment=EMEA, Send Email 1
Probably makes more sense to start in Asia, but you get the idea.
I heard Marketo is working on time zone of recipient (like Mailchimp has). Not sure when though. Mailchimp typically based it on location (reverse lookup) and time of open/click.