Series time line.

[mmmmmmm]

You can't answer this one without spoilers

Spoiler

Dutiful is presumably born approx 9 months (unless fitz is completely wrong about his paternity!) after the end of the farseer trilogy and is 14 at the beginning of fool's errand therefore the gap is 15 years give or take a few months.

The fool states in golden fool (when discussing the Bingtown delegates with fitz) it is two years since he was on the rain wild river and this is after the dragons are hatched so that would perhaps indicate TM starts a couple of years after LT ends given that GF probably covers several months (there is a line in which Fitz says something about spending 6 months teaching Dutiful & being Lord Golden's servant)

The reason I think there is a 6 year gap between LT and dragon keeper is because Thymara saw the dragons emerge from their cocoon and she says this occurs five years earlier when she was almost 11