40min is quite a long time for a presentation unless it's a keynote. I'd suggest 30min total, i.e. 25min talk + 5min questions, and just make sure we stick to it and don't overrun. For the lightning talks, we should differentiate between the true lightning talks (i.e. the sort of talks about someone's plans, which might take 5-7min to talk + a few minutes for questions/comments) and the short presentation types, which might be 15min talking + 5min questions.