Tell them if a shop takes them 1 day to cook their meal and they can only eat tomorrow see if they like it or not.

Else you give them option, say you can fix it outside, still maintain their warranty with letter signed by both parties because you need to use the car. Thats the only viable win win solution. Because they stick to their 1 month or whatever time they want for 1 stupid part.

Else you say see you in tribunal or court or whatever.