Mahabharat really happened or just a story.that is irrelevant.We need to focus more on what Ved Vyas is trying to teach us.Lord would have made this possible because of his "Maya power."When we can find logic in Lord lifting the Govardhan mountain with little finger for 7 days.........a baby killing pootana.......viswaroopa darshanam......etc we can find logic in teaching gita in middle of the battle field too.
The eternal battle in us .......between the the good and the evil forces. Always the number of good is less and the evil forces more in us. Pandavas are 5 and kuravas are 100 in no.Pandavas represent our 5 sense organs.
since it is a study group ask them to analyse why Ved Vyas placed Geeta chanting in the midst of war and not in brindavan.
we have to fight the battle of our life.
We have to fight if we want to realise "aham brahmasmi"

Hari Om,

Rephrasing your question a bit. Are you asking whether it is really possible to have discourse of Gita in between 2 armies at war?

Not sure about impracticality. It appears impractical from "our standpoint & understanding".

From standpoint of Lord Krishna a lot was accomplished. Charioteer & mentor Krishna was able to remove delusion of Arjuna and guide him to win the righteous war. Avatar Krishna was able to uphold the Dharma and save the righteous people on the planet. Jagadguru Krishna through Veda Vyasa continues to guide so many seekers to Moksha.

Coming to your question. Firstly, we are trying to see this from the modern warfare where the the only goal is destruction of enemy by any means and as soon as possible.

Unlike this, in the era of Mahabharata, just before the start of Kali Yuga, there were some rules of conduct even for war. Unarmed fighters, person not willing to fight, PoWs were
not to be harmed. The war had not begun and seeing Arjuna, commander of Pandava army coming to the centre of battlefield may have been construed by Kauravas as trying to
reach an armistice or truce. If you read Mahabharata (Bheeshma Parva?), after Bhagawad Gita was spoken and Arjuna was ready to start the battle, Yudhistra went to Bheeshma and Drona to seek their blessings.

Secondly, the "long dialogue" which you refer maybe our idea based on the number of verses in the chapter. It may not be true indication of time.

The Bhagwad Gita has many verses on Sanjaya's commentary, descriptions of Arjuna's condition, Arjuna's experience of Viswaroopa Darshan. The names are end notes of chapter are in my opinion later addition to recite from memory. And is written in a metre to be poetry. So I am guessing actual time spent in between the armies may not have been much.

Mahabharata is an Itihasa and it is also considered the 5th Veda. There are so many astro/archeo evidences about the events in Mahabharata by which you can determine the exact days of the events. And there Is a day for remembering the day on which it was spoken, it is called Gita Jayanti.

What is important is the teachings of Lord Krishna are available. It is for us to follow it and move from Moha to Moksha!

श्री भगवानुवाच
इमं विवस्वते योगं प्रोक्तवानहमव्ययम्।
:
स एवायं मया तेऽद्य योगः प्रोक्तः पुरातनः। 4.1-4.3

The Blessed Lord said I taught this imperishable Yoga.. that same ancient Yoga has been today taught to thee by Me.

Pranam

ps:
Gita Jayanti falls on 8th Dec 2019. It would be great if MGML could be scheduled on 7,8 Dec 2019!