About 5:20 + 38 = 5:58 min/km on the climb, and 5:20 - 24 = 4.56 min/km on the downhill (you don't get back everything).
Very approximate formula for starting point. Can be more or less, depend on how well conditioned you are for uphill and downhill. Need to train a lot to get use to those, as both uphill and downhill needs different muscles than on the flat. They fatigue more quickly if not trained. 13 km stretch of that climb is a lot. Forget the formula, need to train and learn your pace/effort (or HR) for the slope.