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We reconsider the issue of the number of e-foldings before the end ofinflation at which observable perturbations were generated. We determine aplausible upper limit on that number for the standard cosmology which is around60, with the expectation that the actual value will be up to 10 below this. Wealso note a special property of the $\lambda \phi^4$ model which reduces theuncertainties in that case and favours a higher value, giving a fairly definiteprediction of 64 e-foldings for that model. We note an extreme (and highlyimplausible) situation where the number of e-foldings can be even higher,possibly up to 100, and discuss the shortcomings of quantifying inflation bye-foldings rather than by the change in $aH$. Finally, we discuss the impact ofnon-standard evolution between the end of inflation and the present, showingthat again the expected number of e-foldings can be modified, and in some casessignificantly increased.Comment: 7 pages RevTeX4 file with one figure incorporated. Minor updates to  match version accepted by Physical Review

How long before the end of inflation were observable perturbations produced?