The Indian Railways also have its share of delays just like some countries' trains. Some trains like the Guwahati-Trivandrum Express and the Kir Asr Express are known for the delays in their trains. Both trains can be as late or delayed as 12 hours, which can be surprising for tourists. So it's best to ask around or research about these trains before riding one so you'll know how much time you should allot for the trip.
Then other trains run fairly on time. For example, the Jaisalmer-Delhi Express is known to have punctual times. And if they are delayed, it's not by hours, only by minutes. I imagine trains with shorter routes might be more on time. But it depends on the time of the day and the season as well.
The Indian Railways have actually started monitoring the times of travel of trains through the Integrated Coaching Management System. So maybe in the future, there would be less delays in the trains.