When does a player reveal the existence of a 2nd Lieutenant Order? Do do so during/ after deployment when the unit is on the table? Or only during the order count step in 1.4 of your Active Turn?
Lieutenant orders are generated during the Order Count phase along with Regular orders and Irregular orders, etc. Prior to that your opponent will not be privy to whether your LT generates 1 or 2 LT orders.
From the wiki "Lieutenant Order", it says its open. Information. So, when you're counting order or before or after, whenever the opponent asks you to show your orders. Not who they are from but what orders you have. So the average player will be able to figure out which of your units is providing a 2nd Lt order if their is one. Except for those who have Holomask or marker state. Special Lieutenant Order This Order is not included in the Order Pool, but is kept separate for the Lieutenant to use. The status and expenditure of the Lieutenant Special Order is Open Information. IMPORTANT The status and expenditure of every Order is Open Information. Players must place the Tokens for each Order, including the Lieutenant’s, where all players can see them. Moreover, they must warn their opponent when they are going to using it to activate their Troopers, including the Lieutenant.
Arguably, the LT orders' status can't be open information before they exist, though, so whether it's one or two LT orders will be known only during the player's active turn from Order Count and onwards.