buildTz :: Tz -> Builder
buildTz (hh, mm)
  | hh >= 0 = singleton '+' <> dec2 hh <> singleton ':' <> dec2 mm
  | otherwise = singleton '-' <> dec2 (abs hh) <> singleton ':' <> dec2 (abs mm)
buildTz :: Tz -> Builder
buildTz (hh, mm)
  | hh >= 0 = singleton '+' <> dec2 hh <> singleton ':' <> dec2 mm
  | otherwise = singleton '-' <> dec2 (abs hh) <> singleton ':' <> dec2 (abs mm)
buildTz (hh, mm)
  | hh >= 0 = singleton '+' <> dec2 hh <> singleton ':' <> dec2 mm
  | otherwise = singleton '-' <> dec2 (abs hh) <> singleton ':' <> dec2 (abs mm)