What is the water clarity? How deep can you see a 6"-10" diameter white disk in the water?
You should be most concerned with oxygen loss rather than stratification. Stratified clear water ponds can have dissolved oxygen(DO) in the deep water if light can reach these areas for phytoplankton, periphyton and or submerged vegetation to create DO. Rate of DO loss will be dependent on the biochemical oxygen demand of the water and water clarity.