Any changes you make only affect new flights that will still be generated. Flights that are already generated byvthe system (i.e. that show in the flights tab) will keep their old settings. Even if you manually cancel them, as there cannot be 2 flights with the same number on the same day, even cancelled ones.
When changing a schedule it’s best to activate with a 3-day delay, otherwise it’s a mess. The immediate activation should be used only when creating a schedule from scratch, and only when you’re sure you’ll fill the plane with just one day of bookings.
If you want the new flights to depart at different time then previously scheduled and booked into ORS fliggts, you have two options
Create flights at different time with new flight number (make sure you cancel old booked flights manually)
After manually deleting all flights of a flight number, go into flight number management and delete those flight numbers. After they are deleted, schedule them at a different time at time when you wish and activate. Those flights will now be booked into ORS. You may want to wait 5 to 10 minutes between deleting the flight number and rescheduling it again and activating it.