Then you’d just sit outside one end even longer. Both leaving early puts you back to where you are now?
I had a look at the running and dwell times, and it seems you could trim some of these back to create a 30 min end to end timing (say 31 mins with an extra min recovery at the end.
So an X;00 departure from Barking could end up at Gospel Oak at xx:30 with an 8 min turnaround to leave at xx:38
Assuming the Gospel Oak starter leaves at xx:23 - you would easily clear the bay platform for the incoming service eventually arriving Barking at xx:53(54) - that would leave a 6- 7 min turnaround at Barking for the xx:00.
Theis is based on a wealth of real recorded running times and assuming just a 30 second stop at each station en-route. Obviously recovery time and extended dwells could be added. But this would eat into the turn around time at each terminus. The timings also avoid conflicts at each end, but not sure they allow much time for freight to be pathed through easily enough, probably slightly less easily than now, which may be why the dwell times and running times are fairly relaxed!!
Edit: This exercise was based on timings achieved with a Class 172 diesel, so a 710 with its superior acceleration and braking could easily keep to this schedule!