Let me first explain what AEM is?
Adobe After Effects is a holistic software from Adobe Systems that integrates motion graphics, digital visual effects, and compositing for use in the post-production processes of making a film. As an across the board solutions, After Effects allows animators and production artists to key-in, track, compost, and animated images, text, and graphics in a complete movie clip or film.
To learn Adobe Experience Manager and instill a deep understanding of the tool, you'll take anywhere around 50 to 60 hours. Also depends on your learning speed some might take only 30 hours to learn the same but i reckon to get your fundamental base strong one needs to give adequate time and practice. Training courses are also available to learn Adobe Experience manager and get certified. Such training courses are designed to make you understand each and every element of the tool and also helps you acquire the certification. You can learn more here. Adobe After Effects Training and Certification NetComLearning