There is no definitive timeline for dysplasia becoming cancer because lot depend on your immune system and oral hygine. However, dysplasia is early pre-cancerous growth and the risk of cancer is there.

My father's ENT had said that any oral lesions lasting longer than a month, after tobacco cessation, quitting betel chewing, abstinence from alcohol and avoidance of irritants like sharp-teeth and foods items know to cause irritation, are potential threats and better to get them screened.