Picture a pile of sand, being added to grain by grain. The exact way it piles and slips is unpredictable, and stochastic. Yet, the general behaviour averages to very predictable, forming a pyramid pile in a way related to the specific grains.
When we look at what dimensions are defined as, they are symmetries under transformation, which simplify descriptions, and are directly equivalent to conservation laws (Noether's theorem). We can picture this where say you move a spinning top one metre to the left, and the momentum is the same. But rotate around the axis or around the middle, and the results are different (ie it has rotational but not translational momentum). Same if something has momentum in a spatial direction: there is an assymetry in transformation. This kind of pattern is the core of what we call a dimension. Space and time are sets of transformations and localised properties within them.
Now consider fractional dimensions, fractals. These represent not simple linear or reversing changes as you move across a system (perform a transformation), but fractional changes. The simplest example is the Koch Snowflake, which can be interpreted as niether a line, nor a plane - it has a dimension of 1.26. Fractals occur everywhere in nature, like the branching patterns of trees or alveoli in lungs (you can see a good explanation of how simple rules generate patterns like this here). (my favourite example of behaviour 'simplifying' across a dimension in a fractional way, is blackhole turbulence)
So. In a block universe evolution is a stochastic fractal, pattern. It is a shape, that's all. Like the shapes sandpiles make. Sandpiles have a shape in 3D,and they have an evolving shape in 4D too.
Personally, I'm inclined to see it not as a single 4D block, but a stack of blocks, in 5D. The Holographic Principle, which explains where the information goes when blackholes evaporate, points to this. We could picture quantum event splitting as branching the 4D block, into an additional dimension.