The current version's help output (flags specific to usnparser start at "-T, --timestamp"):

$ vol.py usnparser -h
Volatility Foundation Volatility Framework 2.3.1
Usage: Volatility - A memory forensics analysis platform.

Options:
  -h, --help            list all available options and their default values.
                        Default values may be set in the configuration file
                        (/etc/volatilityrc)
  --conf-file=/home/vol/.volatilityrc
                        User based configuration file
  -d, --debug           Debug volatility
  --plugins=PLUGINS     Additional plugin directories to use (colon separated)
  --info                Print information about all registered objects
  --cache-directory=/home/vol/.cache/volatility
                        Directory where cache files are stored
  --cache               Use caching
  --tz=TZ               Sets the timezone for displaying timestamps
  -f FILENAME, --filename=FILENAME
                        Filename to use when opening an image
  --profile=WinXPSP2x86
                        Name of the profile to load
  -l LOCATION, --location=LOCATION
                        A URN location from which to load an address space
  -w, --write           Enable write support
  --dtb=DTB             DTB Address
  --output=text         Output in this format (format support is module
                        specific)
  --output-file=OUTPUT_FILE
                        write output in this file
  -v, --verbose         Verbose information
  --shift=SHIFT         Mac KASLR shift address
  -g KDBG, --kdbg=KDBG  Specify a specific KDBG virtual address
  -k KPCR, --kpcr=KPCR  Specify a specific KPCR address
  -T, --timestamp       Print timestamps instead of human-readable dates
  -E, --unixtime        Use Unix Epoch 32-bit timestamps instead of native
                        Windows 64-bit timestamps (loses subsecond accuracy).
                        DOES NOT imply -T above.
  -C, --checktime       Don't show entries with timestamps outside of unix
                        epoch range to reduce corrupt entries
  -S, --strict          Enable stricter checks on record integrity to further
                        reduce corrupt entries
  -O, --offset          Show the physical offset for each record
  -R RECORDTYPE, --recordtype=RECORDTYPE
                        Force version of USN record (2 or 3) to search for. In
                        testing so far all OS's seem to use version 2 records
                        in memory (even 8.1/2012r2 which purport to use R3).
                        As such, default is R2.
  -U, --unicode         Show unicode (utf-8) filenames. Be aware that due to
                        corrupted records there will likely be strange
                        characters in some places. Using -C and -S can help
                        cut this down.

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Module USNParser
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Scans for and parses USN journal records