Congratulations!
Based on my own experience, I've found a temperature of 19-20C works very well. At this temperature they took 2 months to morph and all at a length of about 6cm. (Whether or not this may differ depending on the geographical origin of the newts, I do not know.)
I would add that its important to give them lots of space and plenty of cover - they like sitting in elodea/on top of rocks - and it means theyre less likely to take chunks out of each other. (which they have a habit of doing, even when well fed!)
One of the things I think helped me very much was that they got used to eating frozen bloodworm quite quickly - this made feeding much easier and importantly meant it was easy to feed them a large amount of food frequently (providing water changes were done properly).
All the best and keep us posted!