Delay between when assignment is submitted and when HIT becomes 'reviewable'

I have a pipeline written using boto3 and Python that automatically creates HITs and fetches the responses as they are completed. As part of my pipeline, I periodically poll for 'reviewable' HITs that I can fetch the answers from. However, I have discovered that there is often a significant delay (over 10 minutes) between the time when all assignments have been submitted, to the time when the HIT state transitions to 'reviewable'. Has anyone else experienced this delay? Is this just something I need to learn to live with?