If you have turned on the multi-tweet feature in your paper settings, up to two promo-tweets will be sent to your twitter account. In some cases, the second tweet will not be sent.
The option to promote your paper multiple times will be available only if you've chosen to include either hashtags or mentions in your promo-tweet for your paper edition.
Why this condition? Sending a duplicate tweet, even if the promo-tweet is hours apart, is not considered "best practice". By turning on either hashtags or mentions, your post will be slightly different.