Wilderness is anything but static. As hours pass, the sun continues its course. Some creatures go to sleep, others awaken. The sounds change. The air chills or heats, wind picks up. Nightfall makes travel different (Will they stop to camp ? Continue with torches or lanterns and risk attracting beasts ?).
Also consider fatigue. "Realistically", not everyone in a group is going to be able to walk for hours on end (ok, depending on your party, they may). Have them stop for lunch.
Do they know exactly where the entrance to the dungeon is ? Maybe they need a guide who will complain after a while or refuse to go further than some point. Maybe he's the chatty type and insists on relaying details of his history of gallavanting (look to Lyndon from Diablo III for inspiration).
Random events. Including encounters (hostile or not, maybe they cross paths with a merchant caravan ?), but also environmental : the bridge has fallen to disrepair, how will you cross the river ? Especially relevant if the rogue has been dying to use his "Knowledge: Engineering" skill for the last few scenarios. Have them arrive at a point where they will need to search an area for some time. This is the ideal time to have some scouts stumble upon them if appropriate.