"I got this thermos for free" Appears beautifully ordinary to me. "That thermos was for free" Appears undesirable: I would just say "That thermos was free." As the above mentioned commentator indicates, you can never ever say "inside the Saturday afternoon" -- but I do think you now know that. https://docs.google.com/spreadsheets/d/e/2PACX-1vThQYloKZWldp-SOKX4OjBXwRfrgWYaDRrLVem32lfKHmI8mCJiHgR2_0HftTtEvIaeLQv1auoUjdAn/pubhtml