I can't estimate the time, but I built a 1/2 acre pond with a JD 550G dozer. It took a lot longer than I could imagine, and I had a JD 410E backhoe as well. So much depends on the topography, soil types, and water infiltration (as well as the operator). I hit springs which kept flowing in the driest weather and required me to trench in a drainage pipe to the bottom (still stayed wet at the bottom). As a disclaimer, I was learning to use the equipment during this build. I also took great care with the clay core and liner using a sheep's foot roller which has worked out great for me; tight as a drum all last summer. Good luck!
