I find our days are totally unpredictable. Tuesday was a nn day (after two nap days in a row and a 11 h night disturbed by cough), he was in preschool but didn't take the nap they offered. He was shattered in the evening, and we did a bt earlier than half an hour. However, the subsequent night was disturbed by cough and little less than 11 h, absolutely not enough according to me... But the behavior on Wednesday morning was very good. So

Wednesday he napped at preschool, don't know how long but I guess a good nap as he was so well-behaved in the evening. I put him to bed 15 mins before the usual bt, as I knew he should be tired from the previous days and... I had to wake him at 11.5 h!

What is so strange is there is not any correlation between having a nap or not and the night sleep. I think we have to accept to have some up and down in this transition. Following his leads seems to work now, but it makes life less predictable...