Scheduled email not sent - too short time?

I created an email this morning to go to users in Hong Kong in their time zone. It was scheduled to go at 5:45pm local time (9:45am GMT) and we approved it around 9:20am without any problems however we've looked back at it now and 0 emails have been delivered.

I know Marketo can take a while to process emails but there were only 800 in the smart list. Is there a cut-off time for scheduled emails to make sure they go out on time?