Credits are given every time you distribute a song. Regular Credits are NOT added immediately upon marking a release for distribution! The credits arrive in your account as early as 4 weeks prior to the selected release date for your release.
Credits always arrive in your account before your release date.
The closer your release date is to the current date, the sooner you'll get credits.
Example: If you uploaded a release today and set the release date for 1 week from today, you'll get your credits added within 1 week.
On the other hand, if you set your release date in 2, 3, 4+ months in the future, the longer it'll take to get the credits for those releases.
Example: If you uploaded a release today and set the release date 6 months in the future, the earliest possible date you can expect to receive your credits is 4 weeks prior to the selected release date (at the very earliest).