My practical answer is to start with a small amount and see how it feels. Some people tolerate collagen better with food. If it causes bloating or nausea, I’d rethink the product, dose or timing.
If the product tastes weird, smells animal-like or leaves a film, I’d try hiding it in a stronger drink or switching brands. Mixability and taste are not superficial details if the goal is daily use.
I care more about consistency than perfect timing. Morning works for many people because coffee or breakfast is already a habit. After workouts or at night can also be fine if it sits well.
For fasting questions, I’d be honest: collagen has calories and amino acids, so it probably breaks a strict fast. For a looser routine focused on appetite control, some people may still use it. The answer depends on what kind of fast you mean.
The best way to take collagen peptides is the way you can repeat without thinking too much. Coffee, tea, oatmeal, yogurt and smoothies are all common. If it clumps in cold drinks, I’d mix it with a little warm liquid first or use a shaker.