Hi,
In the MIKE ZERO Toolbox there are tools for converting ESRI ASCII raster grids to dfs2 files, meaning convertion between ESRI raster format and DHI raster format. If you want to add the time dimension, by getting a time series from a time varying grid, then you would have to use the DHI SDK for reading and writing DHI files (dfs files). Look at http://www.yourepeat.com/watch/?v=q3pfVKRgI6g for more information.
Oluf