If I’ve shorted the 26300 CE today and I’m up Rs.2,000 per lot at 3:29 PM, and I want to convert this naked short into a credit spread before market close — which strike should I buy, and what’s the logic behind choosing that strike?
The greeks and consequently your PNL profile would change drastically depending on how wide or narrow the spread is. 
The wider it is, the more it resembles a naked short. 
Play around with the strikes in Sensibull, 100 strikes are more liquid than 50s. So at least 100 point wide is how I would do it. 