My DS tried to drop his sleep when his sister came along (2yrs 2months) - but I worked out he still needed it and as long as I had given him lunch and he was comfy - he would still drop off just watching wiggles or something which saved me a fight with a newborn! He day slept until around 3yo.

However my DD has always been too busy and dropped her day sleep around 19 months too ....

I would suggest taking each day as it comes and if they look tired, give it a go, but don't worry if it is not every day.