Yes! Sounds like you are on the default, daily digest delivery schedule. On this schedule FeedBlitz checks your content once a day, around 1:30am in the time zone you picked. Posts selected for inclusion in the daily digest are the ones dated from midnight to midnight. So if your post is dated just after that midnight cut-off it won't be sent for another day.
There are some simple changes you can make to get mailings out sooner. All of these settings can be found under the Newsletter's Settings
From your account dashboard, select your newsletter. Next, please select the “I Want To” button in the upper right area of the page.
Select “Settings, schedule” from the drop down menu. On the next page, click the blue hyperlink that denotes the frequency of your mailings.
Please remember that some blogging systems (notably Blogger) can get time stamps wrong if you draft ahead of posting. Make sure that the posting date reflects the time the article goes live. You can see how FeedBlitz has interpreted the timestamps on your feed by selecting “Troubleshoot” from the drop down menu in the “I Want To” button, then selecting “Diagnose” on the next page.
If a mailing has been "missed" you can always force it out by sending an on demand mailing. Step by step instructions on how to send an on demand mailing are available at the following link: http://support.feedblitz.com/customer/portal/articles/1971325-send-newsflash-on-demand-mailings