You can use time but in the end you need to be able to complete the race distance. This is always a conundrum when it comes to prepping for a very hilly race. 4000 feet of vert in 26 miles is a lot. You might want to consider using the Big Vet plan as it is designed for hilly races of all lengths. But if not then I’d make at least the one long run each week for distance and not time. Others can be for time.