His manager was definitely a power-move playing prick (although probably this way because he himself was insecure within the organization) and, unfortunately, t

His manager was definitely a power-move playing prick (although probably this way because he himself was insecure within the organization) and, unfortunately, they are exactly the sorts of people who turn estimates into deadlines. Decent managers don't say "I need this by end of day" unless the project really is company-existential. If the manager was asking in good faith, he'd have explained why he was asking for the estimate and what decisions would be made based on it, and give the employee allowances to give timeframes that no one would he held to... but it doesn't seem like he was that kind of person.