Please see [this][1] feature request where this behavior was changed from what you're requesting to a system with different dates for each newsletter. Note the [accepted answer][2] describes how the arrival date is chosen for your newsletters. Specifically,

>Instead, newsletters will be staggered across the workweek on a per-user basis: your first newsletter subscription will arrive on Tuesdays*, your second on Thursdays, third on Mondays, fourth Wednesdays, and fifth on Fridays. Your sixth subscription will loop back to Tuesdays, and so on.


  [1]: https://meta.stackexchange.com/questions/99782/dont-send-all-newsletters-on-the-same-day
  [2]: https://meta.stackexchange.com/questions/99782/dont-send-all-newsletters-on-the-same-day/100194#100194