Sea level is usually defined as 0ft. The places on the earth above sea level has positive elevations while the places on the earth below sea level has negative elevations.
If we graph eac level on the number line, it would look like this:
Looking at the number line, the times closest to sea level are those corresponding to - 0.5ft and 0.5ft.
Therefore, the times are noon and 8pm.
Therefore, the times are