Based on residual balance of mass karma of entire humanity as of today it can be safely assessed that Kalki Avatar would surface anywhere between 2022 and 2025. The advent of Kalki Avatar would be directly based on occurrence of world war 3. No sooner it starts, Kalki Avatar would surface immediately.
Even in Dwapar Yuga Lord Krishna advent in the battle of Mahabharata when he delivered sermon of Bhagavad Gita to Arjuna.
An avatar as per Hinduism scriptures is always one amongst us but powered by truthfulness and also jnana wisdom of Bhagavad Gita and Upanishads (independent spiritual treatises). An Avatar truly is a deadly combination of an enlightened one coupled with powers of Chanakya (the most able administrator in the entire history of mankind). To save lives of millions of countrymen and soldiers Chanakya got 100 kings eliminated in one night.
One without mercy and forgiveness, an Avatar truly is one without precedent. Only when people saw him working did they realize his potential! This one-man army would be instrumental in killing 5.5 million people directly under him. To cleanse the society of its ills, to re-establish Dharma (righteousness) tools of forgiveness and mercy do not work any further.
It is primarily the time for judgement! Supported by 2000 million people worldwide, Kalki Avatar would succeed ushering present mankind into Satyuga, the awaited golden period.