If you give a single number as the option value of these options, that option value will be used for every dimension of the PDE.
If you give a number list whose length is the same as the number of independent variable of the PDE as the option value (yeah this syntax is undocumented but valid), the list of numbers will be used as the option values for corresponding dimension. Here is an example.
All of the statement above can be verified by checking
InterpolatingFunction generated by
NDSolve. (If you don't know how to check, read this post. )
Nevertheless, notice that:
The initial value problem (IVP) solver of
NDSolve is quite robust and we don't need to adjust time step choosing in most cases.
MinStepFraction option for
NDSolve so we still need to adjust sub-option of
TensorProductGrid if we need to control the spatial step size accurately.