There are only two good answers to this interview question, maybe three.
 1. As soon as I give proper notice to my current employer.
 2. When would you like for me to start?
 3. Right now.
"I am having fun here, sharing stories of what I have learned after some 25 years of doing startups, with maybe some observations about the workplace, culture and other things that interest or amuse me,...and hopefully, you."
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