This is how it was counted:

12 Valian hours (a full flowing of both trees)= 1 Valian day

1000 Valian days (12000 hours)= 1 Valian year

100 Valian years = 1 Age of the Valar

Here is how the Valian year compares to the Years of the Sun.

1 Valian hour = 7 hours of the Sun

1 Valian day = (7x12) 84 hours of the Sun

1 Valian year = (7x12000) 84000 hours of the Sun

There are (365.25x24) 8766 hours in a Sun year, an thus:

1 Valian year = (84000 divided by 8766) 9.582 years of the Sun.

The dates of the first flowering of the Trees and the first rising of the Moon.

The Trees first flowered after 3500 Valian Years had passed (or 33530 years of the Sun).

The Moon first rose after 5000 Valian Years (or 47901 years of the Sun).

The Trees thus shone for 1495 Valian Years (or 14322 years of the sun).

tbc

All above information is taken from Morgoth's Ring; The Annals of Aman; Section 1