there are 5 yard jobs and 2 road freights, + 2 other railroads that pass through.
2 yard jobs start in the morning, one will do an interchange/transfer run over the hellgate bridge to queens, delivering a fairly large train to NY&A at freshpond, then return w/ more cars towards early/mid afternoon. the other job will do switching in the yard, some industries around the yard, sometimes bring cars up to hunts point market, or cars back. going up to hunts point market, a caboose is used as a 'shoving platform', as this is a long backup move. that can be viewed from edgewater ave. the market itself is not accesible, you wouldn't want to go there anyway, it can be a zoo. there is a park on the otherside of the bronx river that you may be able to view and photograph from w/ a telephoto lens.
around the oakpoint yard itself there are several road bridges over the yard and streets alongside, however, theft is an issue around there, and police/ railroad agents might stop to question you. the thieves have been known to watch the trains as well. use discretion and common sense.
you can also see trains from the ballfields on randalls is., this is fairly safe and public.
there are 2 other jobs that start mid afternoon. one goes up to hunts point market, the other does some yard swiching and builds up the road train w/ the mixed freight cars. that road train departs much later in the evening, and is better seen along the hudson line. the other road train is garbage only from waste manegements harlem river facility. both trains may follow each other out closely when metro north lets them on the mainline after the evening rush.
there is another job that starts after midnight, but you wont be able to photograph it well, though you may see it work, you don't want to be around there.
the other 2 railroads; CP has a train that comes down from upstate and goes to freshpond, it comes into the yard and runs around its train to face the opposite way to head over hellgate. P&W has a stonetrain in warmer months that comes from ct via new rochelle to freshpond, goes through the yard. either of these can run day or night, but mostly night.
check the NY&A/Metro North forums for previous related topics.