Exactly. What did it do, wait at the platform for two hours until the scheduled departure time, or leave all the people that had booked it behind? In 25 years here I've never seen an early train and the only ones on time have been those leaving the central station in Bangkok in the morning.
When leaving Bangsaphan to travel north to Bangkok by train, which we've done often, we call the station before hand to see how late it will be, and it always is.
Edit: It still takes 7-8 hours to travel from BS to BKK by rail, dual track or no dual track.