Sleeping Less in the Evening

My daughter is almost 8 weeks old. Up until this week the longest she would stay awake between naps/bedtime was 2 hours. The past few nights she has been fighting sleep in the evening and has been awake between 3 to 4 hours.

 Have any of you noticed this change in your baby? Do any of your babies stay awake this long?

I am just wondering if this change is something babies this age start to do or just a phase that she is going through.

Thanks!