You’ll take the lift up to the departures level which lets you out between zones B and C. From there you’ll walk the length of the terminal to zone J. With a brisk walk the total time from train to zone J is about 5 minutes. I’m sure c-w-s knows the exact distances and has timed it previously. The above is my experience from yesterday which was closer to 6 minutes as the lifts were slow, and there was a queue of about 5 groups waiting to checkin. I was from the train to the lounge in about 12 minutes.