No jokes now, project time estimate is a serious matter.

I agree with the steps above, and I offer useful 'trick':
Make customer aware that his/her thinking time also needs to be included, too.
I.e. "I'll need 2 weeks to develop Detailed Specifications *after you finished* reviewing and we agreed on Rough Specs."

Of course you will try to start 'Detailed Specs' right after finishing 'Rough', without waiting, but you need to won time… Like in chess game, to won you need to use your opponent’s time to think about your own next step.

Obviously if you thought you need about 2 weeks to do something and they wasted 10 days reading specifications and responding to your questions, you still need 2 weeks to finish the job, right?

Also, take into account you need some time in the evening to ‘recall’ where you finished last time. I call it ‘time for swap’. And like with disk swap, the more often you swap, the less time is available for a useful work. Looks like a lot of weekend work to me.

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