You can achieve the same by =TEXT(NOW();"MM/DD/YYYY_ HH:MM:SS (\E\S\T)")
which calls NOW() only once. This avoids the (extremely rare) error that may occur at midnight, where the first NOW()
is before midnight and the second is after, yielding a timestamp which is 24 hours off.
Having the timezone outside of the number format makes sense.
=TEXT(NOW();"MM/DD/YYYY_ HH:MM:SS")&" (EST)"
is perhaps optimal.
Letters in a format string need to be “escaped” (the backslashes in the first formula) to appear verbatim. Otherwise they may accidentally act as a number placeholder. Your formula is easer to read with this variant, and you can keep the timzone info elsewhere and fetch it individually for your time formulas.