They are usually all up around 2-3 hours before each game. Although for the Spring games, the manager generally tells the players the night before who is making the road trip to "away" games. We are now to the point that the starters can stay in the game for at least 5 innings.
The starting pitcher will be in there for aroud 4-5 innings depending on how many pitches were thrown. On most team websites, the manager will list the EXACT order of relief pitchers for a game. For instance, the newspaper in Houston everyday tells you who will pitch that day and the order of pitching.
This is a DAMN GOOD site to check everyday. For instance, today were are 3 hours away from first pitch and almost all of the early games have complete lineups