" from the data I have I think it will take at least X amount of time, but I can’t give you an absolute certain answer. What I can do is work as diligently as possible, give you frequent updates on my progress and revise the estimations as frequently as you would like. "

― John Z. Sonmez , The Complete Software Developer's Career Guide: How to Learn Programming Languages Quickly, Ace Your Programming Interview, and Land Your Software Developer Dream Job