I err on the side of thinking that time is not linear but clearly that is a debate which is too big for this situation and probably too big for a brain the size of mine. However, as anyone who has ever done interval training knows, even if time is linear our perception of it isn’t. McAvoy’s rule [number 2] states that a minute during a work interval is approximately twice as long as a minute during a rest interval.
That said, you would be wise to have some sort of schedule rather than just try to “wing it”.
I opted for a 24 hour schedule as I didn’t think I could go significantly faster than that. Even with several reconnaissance efforts for various bits there were significant errors. These are demonstrated if you compare my proposed schedule with actual timings. The most significant were 30mins slower than estimated for Scafell Pike to Wythburn Church and 30 mins quicker over Helvellyn. Although this might seem a minor issue, such things can play havoc with your psyche when tired.
The other issue worthy of note from my schedule was the expansion of rest intervals and even the creation of non-scheduled ones. You or someone needs to be strict with this or it could cost you your successful completion. To some extent a schedule is quite subjective in that split times for various components are personal to your relative strengths eg I am much better on a bike than swimming. Your strengths may well differ. Ultimately though, having to get under 24 hours is totally objective. So, even if you opted for a 24 hour schedule it may need to be varied in parts compared to mine.
Without significant reconnaissance it would be difficult to produce a highly personalised schedule. Even then a recce for one section, if done fresh, will only give an estimate of the time needed if that section actually occurs late on when you are very tired.
Pacing and contingency.
Pacing should be realistic. The main risk of a faster schedule, if you are not up to it, is that you might not finish at all. Although it is tempting to think that if you set, say, a 21 hour schedule and start to struggle you will just slow down, it could be that the early quicker pace will leave you too exhausted to finish.
Similarly if you use a large contingency be aware of the same issue. A 24 hour schedule with a 60 mins contingency is actually 23 hour pace. It is false comfort to have a big contingency if the early quicker pace tires you so much that you cannot carry on.
Finally on schedules, once decided on you may want to produce it for several different start times. There are many factors that may vary your start time at the last minute. It is difficult in the dark and mist, 19 hours in, to keep thinking you have to add 37 mins to all your timings. To avoid this you can produce duplicate schedules at 15 min intervals from your earliest start time to cover starting up to 60 mins late or so.