Flight of the Noldor

In The Silmarillion, there is almost no hint of a passage of time between the departure of the Noldor from Tirion, and their arrival in Middle-earth. The only point where the length of the journey is mentioned is in 9 Of the Flight of the Noldor, where we're told that they had 'marched for a great while in the unmeasured night' (this was after the Darkening of Valinor, so 'night' here just means that they were marching in darkness). The Noldor set out from the central regions of the world, and a very large number of them had to travel thousands of miles into the far north. It's reasonable to assume that this journey must have taken at least several years.

In fact, we have the Annals of Aman to give us some insight into this matter (in Morgoth's Ring, volume X of The History of Middle-earth). There, the departure of the Noldor is dated 1495, and their arrival in Middle-earth is dated 1497. These dates are given in Years of the Trees from their first planting, with each Year of the Trees being equivalent to about 9½ solar years. The Flight ofthe Noldor from Aman into Middle-earth, then, took very roughly nineteen years to complete.

Whether the journey of the Noldor was a 'flight' or a 'return' is a matter of perspective. To the Valar, and the Elves they left behind in Aman, the Noldor were fleeing into the dark East of the world. To the Sindar and other Elves who had remained in the Hither Lands, it was the return of long-sundered kin out of the unknown West.