There are many many nonfiction “how to survive” books about grief, with varying degrees of  scientific evidence to back up their advice.  The most common type is fairly anecdotal in nature, including a combination of the author's experiences, perhaps describing some of their work with grieving people as a therapist, or while working in one variety of helping profession or another.

Courage to Grieve is precisely in this category: Judy Tatelbaum lost her brother at a relatively young age and describes being unable to grieve him “appropriately.”  She reported having intrusive symptoms more than than twenty years later, and much of the book addresses what she calls “unexpressed” or “unsuccessful” grief. The book talks more in timelines than any other grief book I've encountered and one wonders what the relationship is between Tatelbaum's interest in “how long it takes” and how long it took for her. Read more about Courage to Grieve by Judy Tatelbaum