Looks like they are adding people in rounds. This morning I added some friends to circles trying to find out how to get them in then later in the morning all of them were added. I did the same thing again and it had appeared to stop working. Late this afternoon all of the additional people were added.
Basically add everyone you want to circles and make a post. They'll likely get through the invite within a day or less based on my current experience.
Basically add everyone you want to circles and make a post. They'll likely get through the invite within a day or less based on my current experience.