How much time should it take someone to bench press 140kgs if they can bench press 60kgs now?
The amount of time to go from 60kg to 140kg will vary depending on genetics and on the training program (nutrition, workout sessions, etc). 
However, using natural training methods it's fair to assume that even with strict training it won't take less than two years for most men.
How should I structure my training program so that I can reach a 140kg bench press in the least amount of time?
To reach a 140kg bench press, it's important to have a well-structured and progressive training program. Here are some tips to help you design your program:

1. Set realistic goals: It's important to set realistic goals that are achievable but also challenging. Keep in mind that progress takes time and consistency.

2. Train frequently: Train your chest, shoulders, and triceps frequently to maximize muscle growth and strength gains. Aim for at least 3-4 sessions per week.

3. Use progressive overload: Gradually increase the weight you lift over time to challenge your muscles and build strength. You can increase the weight by small increments each week, for example, 2-5% increase in weight per session.

4. Focus on compound lifts: Compound lifts like the bench press, dips, and overhead press work multiple muscle groups at once and are great for building overall strength.

5. Incorporate accessory exercises: Accessory exercises like push-ups, dumbbell flys, and tricep extensions can help target specific muscle groups and prevent muscle imbalances.

6. Get enough rest and recovery: Allow your muscles to recover between training sessions by taking rest days and getting enough sleep.

7. Maintain a balanced diet: Eating a balanced diet with sufficient protein, carbohydrates, and healthy fats is essential for muscle growth and recovery.

Remember that consistency and patience are key when it comes to making progress in strength training. Make sure to track your progress and adjust your program as needed to continue challenging your muscles and making progress towards your goal. It's always a good idea to consult with a certified personal trainer to help you design a customized program that is tailored to your specific needs and goals.