My optimistic target of 35mins

[TheEd]

for the future we should look at a long run of no further than 15 km (of course until you have become stronger)

as for your niggle, it may be calf muscle related, if your calf muscles got fatigued on the long run and you were not biomechanically sound running so far (and slowly) you place the ankle (ligaments supporting the ankle) area under duress

please ice the area and look at doing mild calf stretching as well as massage

when's next important race date?

TheEd