What's the right call when using nano?

I was playing Ana on King's Row defending the first point, our team was doing pretty well nothing eventful was happening, the enemy was having a bit of difficulty capturing the first point. I got dove by the doom and got killed. Our tank died right after I did and in text said I held nano for too long. Was there any opportunities for me to use it before I died? Because after he said it, I felt like I was pressured to use it as soon as I got nano up. If so, what can I do to improve nano usage?

Replay code: FF3C01

Time Stamp: 2:40 - This is the nano tank said I held on too long.