18 month old interesting sleep cycles, normal?

My 18 month daughter has usually gone to bed at 7 pm and is out in about 10 minutes and lately has been staying awake for about 30 - 45 minutes, she also has a bit of a cry now at 430 am and then gets herself back to sleep around 6. When they start having these changes is that indicative of anything or should we change our bedtime routine?