U can clean them anytime during the day.
Hours of sun are best for cleaning using Surya or raum,but it doesnt mean u cannot do it any other time during the day.
Try to clean them during hours of sun,if you are unable to because of busy life or some other factors u can do it in other hours as well.
Personally for cleaning i use raum for every chakra for 9 times on each of them. But stick to the number of vibrations u are comfortable with,with a good affirmation at end.
anytime is good, but preferably IN the sunlight, and during the hours of the sun is a plus. during a full moon is also good for breathing lunar energy into your head chakras during the night.