For what it is worth, if a customer of my previous (salaryman-heavy) employer asked for this, we'd tell them an actual no, which is extremely rare in client relationships in Japan. A contextually appropriate "no" for something which is less absurdly wasteful of engineering time to no purpose would be "That sounds difficult. We could explore options to do it, but perhaps you could accept an hour of downtime in the dead of night" then bargain down to 15 minutes.
For what it is worth, if a customer of my previous (salaryman-heavy) employer asked for this, we'd tell them an actual no, which is extremely rare in client relationships in Japan. A contextually appropriate "no" for something which is less absurdly wasteful of engineering time to no purpose would be "That sounds difficult. We could explore options to do it, but perhaps you could accept an hour of downtime in the dead of night" then bargain down to 15 minutes.