Could Doc Brown travel to see the dinosaurs if he wanted to?
From this we can see a 4-digit year, with no place for ten-thousand, hundred-thousand, or million. This means that the Delorean can probably not travel to dates with more than four digits in the year.
Further, it appears that the clock uses The Gregorian Calendar, which further limits the range in which the Delorean can travel. (e.g. using Jovian or Jewish calendars would change the allowable time-range).
But that just means the system as used by the Delorean is restricted. When Doc built his train, he might have added features allowing him to travel even further in time than seen in the film. Currently we have no information on this, so can only speculate.
Cartoon Series In the short-lived Back To The Future cartoon series (which is not considered canon) season 1, episode 3, "Forward to the Past" they travel back to the time of the Dinosaurs, so it can be assumed that Doc had updated his systems for that journey. However, this is not canon so up to you if you think this counts.