I don't work for the A&A, though I occasionally volunteer there. In all of my railfanning experiences in Arcade, I found it best to get there early (between 6-7AM) because it seems that their freight trains left Arcade for Arcade Junction early in the morning. After going to the BR&P interchange and occasionally switching the AGWAY there, the train would run back to Arcade and continue on to Curriers.
Now, if you find yourself behind schedule (10AM, 11AM) I would suggest you head first to Curriers and then backtrack towards Arcade. Many times the track is visible from the interconnecting roads and if the train isn't in Curriers you can spot it as it is making its way North from Arcade. If you make it to Arcade without seeing it stop in the depot (if it is unlocked), introduce yourself if someone is there, and ask if the train has left Arcade yet. Or call them, which is probably better. They are usually very friendly.
When they aren't busy switching cars they seem to wrap up their jobs in the mid-afternoon. Depending on the number of cars, they might get their jobs done quicker or longer. Now that they have a new runaround track in Curriers it is probably easier for them. (Watching them use a tractor to help work the facing-point spurs was fun but seemed to take more time then necessary.)
And, they usually only run freight on the weekdays and probably on an as-needed basis. Not knowing where in the State you are coming from, giving them a call the day before wouldn't hurt either. As I said, they are generally railfan friendly.
As a recommendation, before you set out take a street map of Arcade and Curriers and blow it up on a copier. Then, highlight the tracks and mark any intersecting roads. That way, you are not fumbling with a folding map or a really large bound state atlas.
Benjamin L. Maggi
A&A Railroad Forum Moderator