Hi there!
You are doing W2S on the basis that the waking is habitual I assume. What makes you think that it is habitual?
Do you think that there is any chance that you may need a routine tweak? Also at this age there is a bit of developmental madness (usually aournd 15-16m and then the 18m SR) which can affect sleep. It may be that you have to just hang in there and ride it out. Tweaking if it is developmental doesn't IME have that much of a positive effect.
Also, any sign of teeth? I think we had canines cutting at this age which caused havoc with sleep.
Your day as I understand it did look like this:
WU: 7am
Nap: 10.30/11am - 12.30/1pm
BT: 7pm
It now looks like this:
WU: 6am
Nap: 10.30/11am - 12.30/1pm
BT: 7pm
I have to say 2hours in the day and 11 at night is not too much to worry about unless your LO is obviously tired from the shorter night yk?
Rather than W2S, if you think that it could be routine related then it's probably worth pushing the nap out and working towards an 11.30am nap for 2hours and keeping BT the same (7pm). How you do that depends on how your LO handles routine change and OT. For us for example, I always increase A time in 15minute chunks, hold for one week and then another 15mins, wash and repeat until I am where I need to be. Others can shift on one jump and their LOs adjust beautifully.
What do you think?
Hena