There are so many studies out there on best times to send an email. The best time to send your messages can depend on so many factors (target, message, industry, etc.). I would recommend doing some googling to find information that fits your industry, target demographic and content. Here are a couple recent reports that I have seen:
Aside from checking the research, you will want to conduct your own tests to see what is best for your company.
As for suggestions on how to send or schedule based on time zone, here's a quick thought....
NOTE: You will need to have a field in your database that indicates the time zone that they are in.
You can create a time zone segment based of this field in your lead database to make pulling reports and creating lists easier. Once you have done this, you will want to create a program with multiple smart campaigns. The campaigns will send the same message, but to different segments (time zone) and can be scheduled to run at the time you want to test for that time zone.
This will send your emails to each of the time zones at different times, but you will need to do a few sends for different times in each time zone to see which time is most effective for that time zone. The message will be different each time so you won't be comparing the same message at different times. You will be comparing different messages at different times.
Alternatively, in the program you could create two smart campaigns for each time zone to A/B test a single message. (Ex. All people in Automotive industry and Eastern time zone get the email at 9 and all people in all other industries and Eastern Time get the email at 10.) This would allow you to test one message at two different times.
Hope this helps!