In Jainism, time is divided into vast cycles called Kalachakras, each of which is further divided into two halves: Utsarpini (ascending) and Avasarpini (descending). Each half is subdivided into six periods called āras.

The length of one āra (time period) varies greatly depending on which āra it is:

• Some āras (like the first and last) are believed to last for countless years (asankhyata years, meaning innumerable).
• Others have specific durations measured in crores and crores of years (one crore = 10 million years).

For example, in the current Avasarpini (descending half-cycle) on Bharat Kshetra (our world region), the durations are as follows (according to Jain texts):

1. First āra (Sukhama-sukhama): Infinite years (countless, extremely blissful era)
2. Second āra (Sukhama): 4 crore crore sagaropam years (very long)
3. Third āra (Sukhama-dukham): 42,000 years
4. Fourth āra (Dukhama-sukhama): 21,000 years (we are currently in this āra)
5. Fifth āra (Dukhama): 21,000 years
6. Sixth āra (Dukhama-dukhama): 21,000 years

Note:

• A "sagaropam" is itself a very large unit, often described as countless years.
• The durations are symbolic and meant to illustrate the vastness of time in Jain cosmology.

Summary: One āra can last from tens of thousands to countless years, depending on which āra it is in the Jain time cycle.