grib/src/main/java/ucar/nc2/grib/coord/CoordinateRuntime.java
public List<Double> getOffsetsInTimeUnits() {
    double start = firstDate.getMillis();

    List<Double> result = new ArrayList<>(runtimes.length);
    for (int idx=0; idx<runtimes.length; idx++) {
      double runtime = (double) getRuntime(idx);
      double msecs = (runtime - start);
      result.add(msecs / timeUnit.getValueInMillisecs());
    }
    return result;
  }
public List<Double> getOffsetsInTimeUnits() {
    double start = firstDate.getMillis();

    List<Double> result = new ArrayList<>(runtimes.length);
    for (int idx=0; idx<runtimes.length; idx++) {
      double runtime = (double) getRuntime(idx);
      double msecs = (runtime - start);
      result.add(msecs / timeUnit.getValueInMillisecs());
    }
    return result;
  }
Get offsets from firstDate, in units of timeUnit
@return for each runtime, a list of values from firstdate