This is the reverse of traversing from the TK lounge to UA flights in C/D. I usually plan for 20 minutes for that as a fast walker. Can be less depending on where in C/D you are or how long you have to wait for the mobile lounge / train. I usually leave the TK lounge 50 mins to an hour before a flight from C/D. Obviously your assumed arrival time on UA and time to deplane you can estimate; I am not considering any of that, just travel time between points in the airport.