How long does/did your toddler sleep at night?and when did they start sleeping less hours?

My 18 month old goes to sleep between 7:30 and 8:30 and sleeps until 7-8 ,he naps for 30-40 mins at 12 or 1 because he's cranky and tired,but these past few days he's been waking up at 4 am and doesn't wanna go to sleep he's just ready to stat his day,should I move bedtime for later? when did your tot star sleeping less?