Buddhism has its own cosmology, astrology, and physiology. What about the time?
Buddhists use Kalpas. Kalpa is a Sanskrit word meaning a relatively long period of time in Hindu and Buddhist cosmology
Generally speaking, a kalpa is the period of time between the creation and recreation of a world or universe. In one explanation, there are four different lengths of kalpas. A regular kalpa is approximately 16 million years long, and a small kalpa is 1000 regular kalpas, or about 16.8 billion years. Further, a medium kalpa is roughly 336 billion years, the equivalent of 20 small kalpas. A great kalpa is 4 medium kalpas, or around 1.344 trillion years.
Kalpas relate to the nature of the universe itself, describing immeasurably long cycles of creation and destruction. Like modern science, ancient Buddhist cosmology described a universe of almost infinite size, variety, and duration
The kalpa is often evoked as an encouragement to spiritual practice, reminding us how rare it is to be born human and to hear the Buddhist teachings. “The dharma,” as one Zen chant puts it, “is rarely encountered, even in hundreds of thousands of millions of kalpas.”
Buddha had not spoken about the exact length of the Kalpa in number of years. However, he had given several astounding analogies to understand it
1. Imagine a huge empty cube at the beginning of a kalpa, approximately 16 miles in each side. Once every 100 years, you insert a tiny mustard seed into the cube. According to the Buddha, the huge cube will be filled even before the kalpa ends•
2. Imagine a gigantic rocky mountain at the beginning of kalpa, approximately 16 x 16 x 16 miles. You take a small piece of silk and wipe the mountain once every 100 years.
According to the Buddha, the mountain will be completely depleted even before the kalpa ends.
In one situation, some monks wanted to know how many kalpas had died so far. The Buddha gave the analogy:
If you count the total number of sand particles at the depths of the Ganges river, from where it begins to where it ends at the sea, even that number will be less than the number of passed kalpas.
Another definition of Kalpa is the world where Buddhas are born. There are generally 2 types of kalpa, Suñña-Kalpa and Asuñña-kalpa. The Suñña-Kalpa is the world where no Buddha is born. Asuñña-Kalpa is the world where at least one Buddha is born.
The current kalpa is Bhadda kalpa where Kakusandha, Koṇāgamana, Kassapa, and Gautama Buddhas are born and Metteya Buddha or Future Buddha will be born.