Flight to CHANGCHUN from SINGAPORE

Hi, I am planning my trip from Singapore to Changchun. Do you all know when is a good time to travel in terms of getting cheaper air tickets? And also when is a good day to travel because if I am not wrong the day that the flight depart also play a part in the pricing of the air tickets. Also, is it more advisable for me to take a budget flight to Shenzhen for example, or any other cities, and then when I arrive at the airport I go and purchase a ticket to go to Changchun from there? Will it save me costs? Please advise thank you all!