From Tolkien Gateway

Time is the life of .[1] The Timeless Halls and the Void are implied to be outside Time. The Time began with Eä and the Valar descending to Arda.[2] Time perhaps represents the sequence of the chords sung by Eru in the Ainulindalë.[3]

The Count of Time begun with the Two Trees[4] (see: Years of the Trees).

The expression Deeps of Time probably loosely refers to the vast extent of Time[5] in the unfathomable past or future, and each specific point is an immeasurable space in the Deeps of Time.[2]

Other versions of the legendarium[edit]

In an excerpt related to The Book of Lost Tales, Tolkien introduced some Ainur who represented the concept of time, and presented themselves to Manwë: Aluin was the eldest of the Ainur and represented Time itself, and his children were Fanuin (year), Ranuin (month) and Danuin (day).[6] The excerpt however was soon rejected and the concept was not developed.

While writing drafts of The Lord of the Rings, Tolkien considered that Time is magically "frozen", or passes in a different pace in Lothlórien , and the calendar didn't advance while the Company of the Ring was staying there; however he changed his mind later,[7] with the characters just losing some sense of time, which continued to flow normally.[8]