You are looking to find out how long it takes for a group membership, deletion or any other change take to make it up to the cloud, via the API and finally appearing in the Umbrella dashboard
On environments with only one Active Directory (AD) server (domain controller), a change usually takes up to ~5 minutes to get processed and sent to the cloud, barring any issues in regards around network latency, processing and also the size of the organization being synchronized. After being uploaded we also execute tasks to update policies and some other references which may take several hours.
Having multiple AD servers might increase the time since the AD servers usually have to replicate the changes between themselves and that usually defaults to every 15 minutes, so the total time might be higher than normal, so you should consider planning for that on top of our average.
For more information about AD replication you can check the following articles:
How Active Directory Replication Topology Works