5pm-7pm is always pretty good weekdays. Haven't tried in the day time.
8am-10amish is quite decent on weekends. Dries up a bit in the afternoon.
Of course, there is never going to be a set time when loot is good, as it also depends on TH level and where you farm. The above times are good for Gold 1 and Gold 2, but sometimes loot is just really bad.
Overall, you don't need to boost just because you are TH9. I rarely do because I'm afraid the loot will be so bad that I'll end up wasting all my gems, plus I rarely have the time. Only boost in Golden Hour if that's the case.
