The research on this stuff says that time estimates are extremely inaccurate and to be avoided. If you manage to stay inaccurate by ONLY a factor of 3.14, that is unusually high accuracy.
Much more accurate are estimates of difficulty or complexity (small medium large, weighted numbers, whatever). The manager can then make an average conversion rate to time (with error bars), and use that for medium/long term forecasting. This is demonstrated extremely accurate compared to time estimation (but it is useless and breaks if you apply time/points pressure to your team, or even let them think in terms of a time conversion rate).
This is not new research. Kahneman's Nobel prize about decisions under uncertainty was in 2002. Put away the superstitions and stop estimating with time!
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