How long will the 144 hour visa be offered

Actually, not. This is the policy started by Chinese authorities several years ago and it has just adopted several new shapes and more generous offers than original schemes within the time. It is actual and it will probably remain so because this option has attracted so many passengers to use China as their transit point and some of them have also decided to stay for a several days, enjoying visa free status in otherwise visa locked country. In other words, you really don't need to be in a hurry because this policy is created to last for many years in the future.