Here's a question: how long is it supposed to take for you to get over something sad? Is a week enough? A month? A year? Can you ever get over it? And does it depend on the particular grief? These questions seem to preoccupy the speaker of "I measure every Grief I meet," in a big way. She's had long lasting grief in her life, and she wants to know if others have, too.
The poem argues against the idea that time heals all wounds, suggesting that some kinds of sadness never go away.
One of the ways the speaker "measures" grief is by how long it seems to last.