Ready, Set, Go … Wait I Don’t Have A Watch!

Chimayo has two candles with him. These candles made by Alec look nothing alike and the wax is of varying thickness and do not burn consistently (i.e. it’s possible that in the first minute 90% of the candle is burnt and in the last 59 minutes the rest is burnt). But Alec however guarantees that each candle burns for exactly one hour. Now Chimayo wants to time 30 minutes because Alec wants to take a nap for exactly 30 minutes. using only the candles Chimayo managed to time 30 minutes. Can you?