Change of tactics for this 2nd 5K. Started off at a faster pace than usual on the treadmill for 5 minutes and then slowed down for the next 25 to ensure I ran for the full 30 minutes. (I remembered after completing my last post that I had actually "power walked" during the first 30 - probably explains my lack of elation after that run.)
Anyway, having completed the post grad consolidation, increased the pace, slowed down and repeated the sequence for the last 1.5 km until the 5K was up. That 5K took just over 45 minutes, 2 minutes longer than the last time but I feel a whole lot better about it. Fewer power walk breaks and less time spent walking - all in all, pretty chuffed with myself.