}
if (timeUnit instanceof DateFrameable) {
DateFrameable df = (DateFrameable) timeUnit;
int unitCount = 0;
for (; startDate.before(endDate); unitCount++) {
startDate = df.adjustRight(startDate);
}
result = new TaskLengthImpl(timeUnit, unitCount*sign);
} else {
throw new IllegalArgumentException("Time unit=" + timeUnit
+ " is not date frameable");