The "Dark Times", the time when the Empire holds sway, the time between Episodes III & IV.

The 'problem' was that Rebels started out with totally new characters. One can't get emotionally invested in the show until one understands the characters. So, Rebels took its time to establish the 'base', and that's good storytelling.

"This essentially confirms my theory from last year: Star Wars Rebels is Kanan’s story."

Actually, rewatching this episode several times made me realized one thing: Kanan might be a terrible teacher, but he's an AWESOME Force user