When I change the time on the repeat event, it becomes a separate event. How do I avoid this?
As soon as you adjust the time of a repeating appointment, you've created an exception. This means that that entry is no longer part of the repeat since a repeat, by its nature, means that same event occurring at the same time over some interval. If you adjust the time of all three meetings then you no longer have a repeating event and you have to make all changes to each event individually.
This may be an inconvenience to you but it's how every program that has repeats works.