this is a bit controversial but is my experience after a awake and whingy constantly feeding dd i tried a different approach with ds
i woke him or offered a feed if he was awake every 3-4 hours in the day time and initially put him down at 7, woke and fed at 10 then fed whenever he woke in the morning 4-5 ish. This helped establish an idea of day and night that dd never had. He is now 3.5 months and i feed when he wants in the day but he has fallen into 3-4 hours between feed, with extra foremilk quick feeds on hot days, and i no longer wake him at 10 he still wakes at 5 am then goes back to sleep quickly.
so to actually answer the question at about 4 weeks or whenever your baby seems to wake up and be alert more i would stop waking and offer when she is awake
With my first I 'fed on demand' but he was so undemanding I never established a good milk supply and struggled with breastfeeding and gave up after 2 months. With my second I fed her every 3 hours between 6am and 9pm (for the first few weeks), then fed her during the night when she woke up. I found it much easier to breastfeed as I had a better supply. If you are formula feeding its not so much of an issue but she may not be able t go 4 hours between every feed so it makes some sense to try to encourage the longer gaps between feeds to be at night.
2 princess - I think it might depend on how tiny your Lo is. If she were quite a low birth weight then maybe not let her go to long. My DD (now 25wks) weighed 8lbs and midwife said don't wake her. She will let you know when she needs it.
However once DD got to about 7/8 wks I didn't let her go too long in the day so she got the ozs she needed then so hopefully she would not need so much at night.