You can configure a workflow to assign records only on a certain day of the month.
Steps
Open the workflow.
Click on Settings in the top-right.
Under When should this workflow start?, select one of the following:
Specific day of the month → enter the exact day (e.g. 5 = 5th of each month).
First working day of the month → the first Monday–Friday of the month.
Last working day of the month → the last Monday–Friday of the month.
Notes
“Working day” means Monday to Friday.
Records will only be assigned to the workflow on the chosen date but, once in the workflow, the nodes will be processed as per their time delays, sending times, and re-tries due to errors.