as a practical matter as long as you don't take distributions before salary, you can wait until year-end.
consult with a pro to discuss reasonable compensation and registering to file payroll tax returns especially since not only do federal 941s need to be filed but federal unemployment taxes and possibly state payroll tax returns as well. also discuss whether the S-corp needs to carry worker's compensation insurance.
ues can arise when distributions are taken and then some or all is reclassified later in the year as salary.