1F66 stands a further 16 minutes at Manchester Victoria (15:08-24).
The pre-COVID path would have a Liverpool arrival around 15:32, whereas it is now 16:03. I suspect the timings are padded out to cope with platform availability at Liverpool.
It’s all to do with the Covid Timetables and maintaining a 30 min frequency Victoria to York on the North TPE route.
The Newcastle to Liverpool trains run in the normal* path of the NCL-MIA trains through to Manchester Victoria and then picks up the path of what ordinarily would be the Newcastle to Liverpool trains through to Lime Street.
The xx:54 departure from Liverpool is usually* a Scarborough. This gives a longer turnaround at Liverpool to help with increased cleaning (giving 35 mins at Newcastle and around 50 mins at Liverpool). On the return running in the path of the LIV-SCA services as far as Vic and slotting back into the path of the MIA-NCL trains from Victoria giving a 30 min frequency.
1F66 is the oddity due to being extended to Liverpool in the latest uplift (supporting with crew competence on the 68/mk5a). It essentially runs in the path of a normal SCA-LIV service to York, with its dwell at York slotting it into the NCL-MIA path (the Newcastle originating Service terminates and starts back from York) and the same as above into the NCL-LIV path at Manchester Victoria.
If it didn’t there would be an xx:20 and XX:28 departure west from York with a 52 minute gap so the dwells help to maintain even frequency.
The Liverpool’s run in the path of the airports as the other route running fully are the Redcar-Airport trains which gives 30 mins (xx:20 and xx:50)
*=Normal pre-Covid timetable