Hello Piglet. I'm so pleased you finally got your allotment! You have a dilemma really.
If your soil is heavy and has clay in it, I wouldn't try digging it or treading on it too much, if it is too wet. Ours was awful when we first got our allotment, really clay-ey. Shiny clumps when wet, turned into baked bricks when dried out. The plot looked like a scene from an earthquake disaster movie...huge cracks everywhere that first summer.
We have spent eight years double digging and incorporating good horse muck and finally have a decent soil structure, which still tends to be on the heavy side. We use a fork rather than a spade, if it's a bit wet, and stand on a plank to avoid compressing the soil. I'm afraid, we leave the digging if it is too wet.
As Primrose said, the wind will help dry it out a bit...I know you will be champing at the bit to get on though! Please be careful of your back...a little and often, no marathon digging sessions!
Good luck.