There are various systems of online train schedules available. Most are based on the same database and the same system.
These systems are always up-to-date.
Schedules are usually available up to three months in advance.
Caution: small changes are made to the train schedules in early December and in early June. However, these changes are usually relatively insignificant. If you are looking for information about trains on a date after the changes, you will maybe not find the updated timetables. This is why you should just enter the date of the following day in order to find train connections, as these will probably be similar to the new ones after the changes anyways.
There is no special online schedule plan for rail pass travelers. You will have to use the regular online systems.
The following procedure is recommended for rail pass travelers:
1) Look for train connections on railcc - you will find special connections with all important details (trains without extra fees, trains requiring reservations, night trains, ...).
2) If you cannot find the information you look for in section (1), visit one of the existing online journey planners.
3) Choose a connection and compare it to available types of trains, check whether a reservation is required and if the connection is free of extra fees.
With most online schedule planners you can find different versions of connections: for example connections only using local trains (usually free of extra costs), trains without supplements, etc. This information, however, is related to standard single train tickets and NOT to rail passes - but may still be helpful.