3-5 years (in-game time). Failure Conditions: Going bankrupt, losing the mail contract bid, or failing to connect the cities before the rival.
Now the competition becomes a race. Your rival will try to reach the mail contract cities first. You can win through speed or sabotage. railroad corporation first competition walkthrough
Fill every available slot on your primary objective trains. 3-5 years (in-game time)
Avoid sharp curves to maintain optimal train speed. losing the mail contract bid