Yup, its most efficient to use the chunks argument when opening the data, where possible (see here). But this chunking is applied before the combine step in open_mfdataset. In your case, this means chunk sizes in time will be truncated at the length of the time dimension in the files you’re combining.
I think it’s probably a good idea to do all the chunking you can using the chunks argument in open_mfdataset, and only chunk time using the .chunk() method, e.g.,
eslice = xr.open_mfdataset(
paths,
chunks={"time": -1, "zi": 1, "xh": 500, etc},
etc
).chunk(chunks={"time": -1})