Every night.
DS wasn't a brilliant sleeper but we had bad nights and good nights, on a good night he'd go to 3 or 4, on a bad night, well...less said the better really.
But DD goes to bed somewhere between 7 and 8. She then (usually) stays there until between 12 and 1 when she wakes. Why would that be? I keep hoping for a 'better' night but no, every night is the same.