Multiple Email sent after csv file import

I installed subscribe by email and imported a csv file of current members from feedburner. All went well. Most of those users received multiple emails. I'm not sure how to fix this. My current settings are to send email in batches of 300 (1500 subscribers) starting at 1:00AM EST. I got 5 emails. 12:23, 12:25, 12:43, 1:07 and 1:20. Any suggestions on how to fix? Thanks.