I am presently having a go with the timings to see if what I suggested in my previous post would work out if the sleeper was to run via Birmingham post HS2, with portions for Inverness and Fort William uncoupling/coupling at Mossend Yard instead of Edinburgh Waverley.
So far, I have kept the existing departure time from Euston, with additional calls at Milton Keynes Central (11 minute layover, so as to allow the 21:40 Euston-Manchester to overtake). Also calling at Coventry, Birmingham International, New Street (14 minute layover), and Stafford (I have given this a 48 minute run time so as to allow for diversion via Soho South, Tame Bridge Parkway, Bescot Junction, and Bushbury Junction). Timings north of Stafford would therefore be 1 hour later.
One thing I have noticed while looking at the RTT website is that when departing Mossend Yard heading northbound, in most instances it is 10 minutes running time that is given from the yard to Mossend North Exit, even though it is 2 minutes or so in the opposite direction. I am unsure if manual hand signals are used or not.
Also, I have found that for the Inverness northbound, timings from Larbert Junction onwards can only really be moved a maximum of 14 minutes later, as the 02:48 Oxwellmains - Inverness freight reaches Larbert Junction at 05:08 (see
https://www.realtimetrains.co.uk/service/gb-nr:H14047/2021-11-04/detailed), and as it is timed for 60mph max, this suggests a Class 60 loco if I have interpreted it right as that is the maximum speed they are capable of.
Of note, I have got the northbound Inverness train arriving Mossend Yard at 03:48 and departing 04:04 (or 04:08 arrival, 04:28 departure if running 14 minutes later north of Larbert Junction, with a 9 minute layover at Kingussie, 10 at Aviemore, and 11 at Carrbridge so as to allow the first three southbound departures from Inverness to pass) reaching Larbert Junction at the existing time of 04:51 after calling Cumbernauld (05:05 if running 14 minutes later).
With the Inverness retimed 14 minutes later, I still need to reduce timings by 16 minutes or so between Birmingham and Mossend. I'll take a break for a bit and return to it at some point.