They do fire late. They were definitely firing - it was far too regular to be thunder. If the conditions are right it can be pretty loud & you can almost feel it, even from Poole
Maybe you could hear something from one of the channel storms as well.
The tanks were firing at Lulworth - I could hear it from my house pretty clearly. I live on a hill and the sound carries straight across the harbour from over on the purbecks. B-BOOOOMMM