People do take clones during flowering. When I lived in the tropics, we got 12/12 all day all year and the only way to take clones was after they showed sex and stretched a bit, cause they didn't get too huge on 12/12 from seed either. That was usually 3-4 weeks into flowering. It works, no doubt. The idea however is that the deeper the plant is into flowering the more time it is gonna take to develop roots. It works, but is it worth it? Unless situations don't leave you with another option, I'd stick to taking clones shortly after (if not right when) they show sex.