Normally speaking, we say that a volume
has three dimensions
, a surface
has two dimensions, a line
has one dimension and a point
has zero dimensions. By this reckoning, an instanton
has -1 dimension.
A point, which persists through time, has one dimension more than an instanton. As soon as an instanton is there, it is gone. It is a true point in four-dimentional space-time (or, often, in higher-dimensional constructs, in the work of many theoretical physicists.)
We might suspect some gross error in dimensional analysis, of the 'off by one' kind, given the implication of a negative dimensionality according to the prevailing convention, but in fact, as Gorgonzola has indicated below, geometry itself takes no heed of temporal dimensions - though of course it may be used to represent them - all its structures and representations are static and eternal, perpetually true in Platonic heaven...