Some more context:
I would be landing at the airport at 8.30 AM and am planning to go to Kandy straight from the Airport by road, explore the city till it gets dark, and next day catch the 3:30 AM train from Kandy to Ella. From what could I see, it is relatively slower compared to other trains(6hrs30 vs 10hrs). But I am confident that I'll get a seat at 3.30 AM :p
Apart from this information, I could not figure out the margins by which it can get delayed, like it is known that the express trains usually run can get delayed by and hour. So any piece of information in that regard would be really helpful.