I would recommend you assessing the time commitment/reward by attending an Thunderbird part-time information session and speaking with people at your company who have completed the program.

You could also quantitatively analyze the decision by for example determining if people have received pay raises at your company. Overall, though if your company is paying for 70% I think you might as well start the program because the business perspective will be very helpful. If the time commitment is too great you would still have the knowledge and could always continue at a later date.

Good luck,