Mine seem to think its a great time to drop them because I could really use a day sleep around that age because I pregnant with the next! Evan was always hard to get to sleep so when it became really hard we just stopped pushing it because come 4pm he was either still asleep or not at all. Once the sleep got as late as that, bed time became an issue. So I made a rule that 2pm was the cut off to go down & up by 3pm.
just to freak you all out even more, we don't get day sleeps AND my kids don't go to bed till 8.30, even Isla! She sleeps in well though.