There is really no way to know if a ride will open early or not. In general, it's best to go under the assumption that a ride will not re-open early so you won't be disappointed if it does not open. They won't announce that the ride is open and, often the times board in the parks will still have the ride listed as down for maintenance. That's what happened with PotC last week...it was slated to be closed through Thursday (opening on Friday), but it opened on Thursday afternoon. The times board listed it down as undergoing maintenance even though it was running. Small World, on the other hand, did not open early. So it's totally hit-or-miss.
In my experience, if rides do open "early" it's the day before or so and not necessarily for the entire day. When rides go down major overhaul/rehab (like Big Thunder) there is a better chance of a soft opening. For rides going down for regular maintenance, it's harder to say if it'll open earlier.