It was tiring, it was a big mental drain, it was for sure, physically very challenging. But at the end of the day, I made it though the 32K in about 3:57 (hr:min). I took small 2 min walking breaks every 20 mins or so, and ran conservatively. After this, I would dare to predict my marathon completion time as 4:40, plus or minus 10 mins. 13 more days, and we will find out how accurate I was.
BTW, I also got my acceptance letter from Mumbai marathon today, and they say that anyone completing the full marathon outside 5 hrs will not be getting the timing certificate. Actually they didnt say that, but mentioned that the marathon starts 08:00 and anyone finishing after 1:00 will not get that certificate.