Ian will be 3 in 2 months. Since the time change, a few weeks ago, he seems to need much less sleep.
On a normal week day he gets up around 6am and goes to sleep around 9pm (although I put him to bed at 8)..+ he sleeps 2 hours in the afternoon..makes 11 hours total.
That seems very little to me..especially because just a month ago he would just fall into bed at 7:30pm , and sleep 3 hours and more in the afternoons..so that's about 2 hours more sleep.

All this would be cool, but what bothers me is:

- the nanny wakes him up after 2 hours (because I ask her to), and he's usually in deep sleep then. I hate waking him.
- but although he seems to need more sleep in the afternoon, he still has a real hard time falling asleep in the evening.
- and in the morning he wakes up on his own.

Am I doing something wrong ?

You are soooo lucky...neither of my children napped after age 2 unless I had no intentions of getting any sleep that evening.
Your son will sleep as much as he needs to on his own...and you will know when he's not getting enough(he's cranky)or when it's time to cut out the naps (he won't sleep at night...the warewolf comes out and it's time to be very naughty).
Everybody has different patterns...

I don't think you're doing anything wrong at all. Maybe the time change kinda messed up his sleep cycle a little, but I think he's getting plenty of sleep. My 4 yo will wake at 7 am (even on weekends, yuck) and not always nap and not go to sleep till 9 pm. But if she needs a nap, she takes one. (She naps every afternoon during the week) Maybe it'll just take a little more time for his little system to get the kinks worked out from the time change. I messes with my system, too.

I think time change messes up everyone. I am a firm believer in sleep schedules for kids and for the most part try to keep them to it. Of course there are times when it does not happen but for the most part I do. One thing that has worked for me is shifting there times if they can't go to sleep at night.
Instead of putting them down for a nap at say 1pm I will bump it up to 12 so they get up earlier from it then they will go to bed at night earlier. They are getting the same amount of sleep I am just shifting it around.
Something else is he may not need as much sleep with the longer days. I do not sleep as much in the summer as I do in the winter.
Normal sleep hours for a 2 to 3 year old is 10-14 hours of sleep. So as long as he is not acting tired I would not worry about it to much.
I really do not see where you are doing anything wrong at all. Every child is different too.
Some of my kids need more sleep than others. I have some that wake up at 7am and go to bed at nine. When they were younger around 4 stopped napps for the most part. I now have an almost 6 year old that for the most part still takes naps and goes to lay down on his own. He will sometimes sleep longer than the 3 year old at nap time, and go to bed sooner for night time, then wake up later. He just needs more sleep.
Something else to consider is he making a point of staying awake? Doing things to insure he is awake so he does not miss anything. He is at a good age for it.
Best of luck to you. Like I said I do not see where you are doing anything wrong at all.