Is there ever a right time to ask a superior for a letter of recommendation?

Emails can help. 

Of course, when they're busy, it's best to let them be and choose a time that's more appropriate if you're doing so in person. 

So what's the right way?

On That's How! Roshan Gidwani uncovers some key points that can help you figure out how to ask for a letter of recommendation. 

Source: https://sg.indeed.com/career-advice/career-development/how-to-ask-for-a-letter-of-recommendation