Generally a straddle must be made/placed before cards are dealt. You really need to check the House Rules to answer the 2nd part of your question, but in my opinion, to allow a player to post a straddle at any time as long as players have supposedly not looked at their cards puts unnecessary pressure on the dealer. How can the dealer know for certain that all players have not looked at their cards.
If a player can't get his straddle bet placed timely, he can always declare "Straddle" and put the chips out promptly thereafter.
But again, you need to check the house rules AND from my perspective, it does no good to argue with the floor over the house rules. They are what they are and cannot be changed "on the spot". You can file a complaint or request a discussion with the manager, but that isn't going to happen right away.