At 18mo DD was in that awkward transition from two naps down to one.
On a good day I could keep her up til 11.30, give her an early lunch and she would go down 12-2.30. On a bad day she would have a nap, 9.30-10.30, then go back down 1.30-3.
Both situations she would sleep 7pm-7am (no wakes).
On the very very rare occasion she didnt nap at all (my mum minding her and 'deciding' she no longer needed a nap), DD would go down at 6pm and wale every two hours through the night.
Sleep begats sleep in her case.