If I have a rogue who fires a ranged weapon as a sneak attack, then passes his stealth-20 check to snipe, can he then make a second ranged sneak attack on the next round? If so (or if not), what is the justification? I haven't been able to find anything that makes this point clear, but the two opinions I have found seem to be 1) Yes, because the rogue is still hidden and 2) No, because the enemy is no longer surprised.
Sadly, the RAW answer is no. You can snipe and remain hidden, but your next attack is not a sneak attack because "stealthed" isn't a condition that makes a target flat-footed or denies it its Dex bonus to AC. Similarly, if you simply stay hidden until the battle is raging and try to shoot someone, it's not RAW a sneak attack. (It's not because it doesn't say it is, the rules are clear in omission.)
Of course this tends to defy reason, so I let people get in sneak attacks in other situations, as "it's the first round of a combat" is not a real in-game-world thing.
The devs understand the stealth rules are a big hot mess; in fact they posted some playtest new stealth rules on paizo.com in an attempt to come up with something less wonky.
Sniping on SRD Action: Usually none. Normally, you make a Stealth check as part of movement, so it doesn't take a separate action. However, using Stealth immediately after a ranged attack (see Sniping, above) is a move action.
Since you spend a move action on the stealth check (and presumably a standard on the attack itself) you cannot full attack. so one attack per round
Edit: In following rounds, assuming the enemy is still hasn't spotted you you can still land sneak attacks since the opponent can't see you, works like invisibility or similar situations