Each exposure is 40 ms. The EPIC camera images at 317, 325, 340, 388, 443, 552, 680, 688, 764, and 779 nm. It transmits one photo of each spectral slice every hour.
I would guess that channels used for a composite color photo for human-eye viewing would be 443nm (blue), 552nm (green), and 688nm (red), but 680nm is also a visible color (red). The NASA article also implies that one red or the other is imaged first, and green is last, so they are not taken in ascending or descending wavelength order. It is also ambiguous as to whether each spectral slice is 30s apart, or whether it is 30s total timespan between the red and green slices.
I would guess that channels used for a composite color photo for human-eye viewing would be 443nm (blue), 552nm (green), and 688nm (red), but 680nm is also a visible color (red). The NASA article also implies that one red or the other is imaged first, and green is last, so they are not taken in ascending or descending wavelength order. It is also ambiguous as to whether each spectral slice is 30s apart, or whether it is 30s total timespan between the red and green slices.