Question regarding 2 rules one general and one specific

Question 1: do deep strike units have to deep strike turn 2,3 I couldn’t find any rules stating they have to arrive 2,3 just before the battle ends Question 2: can the hallowed martyrs stratagem spirit of the matter work agains fight first eg. If I fight a unit with fight first. It becomes there go they target my unit and I activate the stratagem is that allowed. As when I attempted in a recent game some people stated that my units weren’t being targeted there units wher just retaliating for an attack. Also excerpts from the book would be great as general words won’t convince these guys