Hi Stephanie,
Please see my comments below to your questions.
1. Based on this
guide, it may take up to 6 to 12 hours for your list to be actually populated/updated with members. Basically, if you have 3 requests for adding members, removing them, then adding them again in 2 hours apart per request, then per request will still have 6 to 12 hrs before it is completed. You can make your last request as your point in counting the number of hours for the whole requests to complete.
2. Yes, you can already associate the audience/user list with "In process" status to your campaigns, and it will be successful in the API. However, your audience criterion won't function as intended as there are no members of your audience yet, or it is still in progress in adding members to it.
Let me know if you have further clarifications.
Thanks,
Vincent
AdWords API Team