They can stay in the refuge huts as long as they like. The 30 minute rule is just for Malham Tarn, Horton In Ribblesdale Cafe, Dufton Village hall and Forest View Byrness.
They are going to be desperate for some sleep at Bellingham, so arriving late, i.e. with only a couple of hours to spare and knowing you then have no chance without bivvying until Hut 1 is going to mentally tough.