It’s all depends on your driving however if you have the time do it at 30. And be prepared for long time pumping if you use manual pump. If you going to do it at 30 invest in special pump used for liquid that can manually take about a quart I One shot and it’s cleaner. Just did my son’s car and took me long time to pump. Remember to close the plug then start the car till its normal temp then open add more till it’s start coming out. Good luck