Hi
Not sure there is a reasonable time – it is what it is.
Hopefully more helpful: We currently have a replacement car as ours is in the garage. We requested and got an electric so it may be worth asking for that.
Also, be aware of the small print. If it is with Europe Car (I believe the provider is changing) the first month is unlimited mileage but if you have it for more than 28 days there is a mileage limit applied to the whole hire time – may not be an issue for you but it was for us 2 years ago!…. Hence we checked limits this time.