This was based on my approach last time. Did Pocklington to Loughton in about 24 hours and got home with 3 hours to spare.Actually, with the diversion at Middleton Tyas, 116 hours, 64 minutes would be OK too.
If @Trickedem has 360km (Pocklington) to go at 0500 Thu, a 1215 start means you have till 0820 Fri to finish.13kph average will get the rider there, or 15kph with a 3 hour kip at St Ives (say). Entirely doable, even with a headwind.
I am expecting to be fairly close to the line a few times.