Its normal for a prem, wait until she is term plus a wek or two and you should notice a difference. Make the most of it! Also, if she has been in SCN they are often 'trained' to wake for feeds at a certain time, a good side effect!
That's what I thought Saffy. I'm definitely making the most of it. What's the bet she 'wakes up' just as DH goes back to work? (He's just started his 2 weeks off). Oh and she is trained quite well too. Pretty much doesn't stir til 3.5-4 hrs since last feed.