As i understand trailing stop may start anytime.
There are EAs where trailing stop is trailing the stop loss. So trailing stop is active from the beginning.
There are EA trailing stop loss if trade is in profit. Some people call it "profit trailing"
So it may be any combination especially together with BreakEven.
Check the links I posted today
trail SL EA
There are some EAs with selectable options: Profit Trailing = true or false for example.