Both tables were adapted from Alfalfa Stand Establishment Questions and Answers. OSU Extension Circular E 949. Obviously these comparisons between proven good varieties and common seed do not fit all situations. As disease and insect problems increase during a stand, the difference paid for seed of improved varieties will be paid off sooner. Also, as price per ton of hay increases, the seed cost difference is paid off sooner.
Higher yields result in shorter recuperation times.
Anything improving profits shortens recuperation time. If yield of both types is drastically reduced because of low soil fertility, it takes longer to recuperate additional seed costs. Lower average hay price would also lead to a slower time to recuperate cost differences. Hopefully you have selected a good site and seedbed preparation are such that you can make a timely planting in early September. This is a major problem when moisture is limiting as it is in many areas this year.