update create and delete feature group API descriptions to mention in-memory tier creation/deletion time

Author: mwfongAWS

doc/amazon_sagemaker_featurestore.rst

@@ -230,9 +230,11 @@ The following code from the fraud detection example shows a minimal
        enable_online_store=True
    )
 
-Creating a feature group takes time as the data is loaded. You will need
-to wait until it is created before you can use it. You can check status
-using the following method.
+Creating a feature group takes time as the data is loaded. You will need 
+to wait until it is created before you can use it. You can check status 
+using the following method. Note that it can take approximately 10-15 
+minutes to provision an online ``FeatureGroup`` with ``StorageType`` of 
+``InMemory``.
 
 .. code:: python
 
@@ -480,7 +482,9 @@ Feature Store `DatasetBuilder API Reference
 .. rubric:: Delete a feature group
    :name: bCe9CA61b78
 
-You can delete a feature group with the ``delete`` function.
+You can delete a feature group with the ``delete`` function. Note that it 
+can take approximately 10-15 minutes to delete an online ``FeatureGroup`` 
+with ``StorageType`` of ``InMemory``.
 
 .. code:: python