MsM and I did a 50-mile challenge walk (think walking Audax, mostly on footpaths and bridleways) at the weekend. I had programmed the route into my Garmin via Tracklogs, so when darkness fell - and it gets
really dark away from roads - we just carried on at the same speed, with her reading out the route sheet as we went, and me interpreting the GPS compass arrow and applying what it told me to what I could see by the light of an LED head torch. It
needs a bit of interpretation, because the accuracy available from 3-digit grid references is a bit lacking - but in conjunction with the route sheet, it worked really well. We only took one wrong turn in 15 miles-worth of darkness, and we knew within less than 100 yards that we'd gone wrong, retraced and quickly got back on route.
We gradually picked up a "tail" of about a dozen people... and when we came out of the next control, we found them all waiting for us
One of them even said "Thanks" at the end