A simple function to calculate the Mars Sol Date (MSD) and the Coordinated Mars Time (MTC) from the current number of seconds since the UNIX epoch.

MARSclock.lua

function mars_time()
  local ms = os.time()*1000
  local JDut = 2440587.5 + (ms /86400000)
  local JDtt = JDut + (35 + 32.184) / 86400
  local J2000 = JDtt - 2451545.0
  local MSD = ((J2000 - 4.5)/1.027491252) + 44796 - 0.00096
  local MTC = (24 * MSD) % 24
  local h = math.floor(MTC)
  local m = math.floor((MTC - h)*60)
  local s = math.floor((MTC - h - (m/60))*60*60)
  return string.format("%0.5f", MSD), h .. ":" .. m .. ":" .. s
end

while true do
  msd, hms = mars_time()
  os.execute("clear")
  print("Mars Sol Date:", msd)
  print("Coordinated Mars Time:", hms)
end

This is NOT platform independent. This function assumes that os.time() returns the number of elapsed seconds since the UNIX epoch. Some Lua platforms behave differently and this script must be modified in such instances.