The questions are:
1.Why Bhisma, Karna and others did not hear Gita even they were also present there?
2.If time was paused, how Sanjay heard Gita?
3.Is there any reference in Mahabharata or Gita, which proves that Krishna paused the time?
An interesting question indeed!!
There are 2 options available , in my opinion, to answer these questions.
- There was no lengthy discourse, which was popularised in the name of Gita. It might be an interpolation.
Sri Krishna might have sternly warned Arjuna of consequences of renunciation of war, by abdicating the duty of a warrior, in quick and yet brief speech. Arjuna might have reconciled.
- Sri Krishna might have stopped the time.
If we accept that Sri Krishna stopped the TIME, as at the time of giving discourse to Arjuna, his mind had been merged into the BRAHMAN and thus he was BRAHMAN/TIME itself, then the question as to how could Sanjay hear Gita? is genuine.
Sage Vyasa gives power to Sanjaya to witness the Mahabharata war to report to Dhritarashtra.
"Upon his not wishing to see the battle but wishing to hear of it,
Vyasa, that lord of boons, gave a boon to Sanjaya. (And addressing
Dhritarashtra he said),--
'This Sanjaya, O king, will describe the battle to thee. Nothing in
the whole battle will be beyond this one's eyes.
' Endued, O king with celestial vision, Sanjaya will narrate the
battle to thee. He will have knowledge of everything. Manifest or
concealed, (happening) by day or by night, even that which is
thought of in the mind, Sanjaya shall know everything. Weapons will
not cut him and exertion will not fatigue him. This son of Gavalgani
will come out of the battle with life. "
So nothing is concealed, whatever transpired in the Mahabharata war, from Sanjaya. That was how he could listen to Gita also.