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.