salaries go out every day (as seen from the income screen) so optimally add the routes the day before. You can always create the routes and schedule them to the plane to check they work, then clear the schedule.
If you have automatic hiring turned on, then when you add the routes it immediately hires the staff, so scheduling and immediately clearing a plane defeats the purpose.
Staff used to be paid weekly on Tuesdays at midday, but is now done daily at midday. Most things in the game are calculated daily at either midday or midnight.
Therefore, if your aim is to pinch as many pennies as possible, the best way is to schedule the plane/hire the staff on the day you will first use it, and do so after midday so that you didn't pay the new staff on that first day.
That sort of micromanagement is generally not so useful after the very early growth phase, the restricting thing after that becomes your time rather than your airline's profit.
The #1 thing you can do to reduce staffing costs, which makes a much bigger difference than anything else, is to set salary increases to manual. Every March 1 you'll get a request for increases, and occasionally you'll get one on Aug 1 too. You can safely leave that request for ~6 weeks before morale starts to drop, then you simply agree to all requests with a single button click, and wait another 12 game months/1 RL week before doing it again. 20 years down the line your staff will be making less than someone who left auto-raise salaries on for 20 years.
