Well the best time would be the time you would need to calm down. It’s best to do it in the morning from when you wake up so you’re not sore and the evening/night so you can just relax till bed. Also if you get bored you can watch tv while you stretch.
Find time within your down time. I tend to stretch in the evening when I’m watching a film. I often get bored stretching if it’s the sole thing I’m focusing on, so having something in the background even just some music can really help me stay consistent. If I know I won’t have time in the evening to fully stretch, just wake up five minutes earlier in the morning to stretch first thing. Your muscles are usually quite warm due to body heat so a deeper stretch can some time be quicker.