The evaporation of sessile droplets with a constant base radius (pinning mode) and a constant contact angle (depinning mode) has been experimentally observed. Here we analyzed the effect of substrate hydrophobicity on the lifetimes of evaporating droplets for the two modes. Theoretical predictions were obtained and compared with available experimental results. The theoretical analysis and experimental results show that linear methods of extrapolating limited experimental data for a transient droplet contact angle and base radius overpredict the droplet lifetime. Likewise, the linear extrapolation of limited experimental data for transient droplet volume underpredicts the droplet lifetime. Correct methods of extrapolating limited experimental data for transient droplet parameters are described, discussed, and validated. The new methods removed inconsistencies in the previous theory and experimental analysis. Master equations and master curves for the droplet lifetime for the two evaporation modes are obtained and experimentally confirmed.