That doesn't work when you can't predict what other tasks might interrupt you between now and date X. That's why estimating in units of effort is much more reli

That doesn't work when you can't predict what other tasks might interrupt you between now and date X. That's why estimating in units of effort is much more reliable than units of time. The drawback to units of effort is that estimates eventually bubble up to non-technical people who don't discern the difference between effort and time, and for most projects there are going to be some time-based constraints on the schedule.