None of quests are on timer. They all have at least 1 mill credit reward, xp/SK reward depends on your level.
You start this quest chain by talking to
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(1), located at 2580x1185 Yutto Marshes. To cover his back, first thing he does is hand you Rubi-Ka Tours Standard Expedition Disclaimer. You need to give it back to him alongside 10k credits (don't worry, you'll get your money back soon enough). Once this is completed, he sends you on first sighting (don't get fooled, tour is just another expression for usual bloodbath).
In order to find desired
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(2), travel to 1080x360 in Valley of the Dead (close to Penumbra-Inferno portal).
You need to kill 5 Weakened Chimeras, 5 Chimera Crushers and 1 Aberrant Chimera. Like most quests in this chain, you need to kill in proper order. That can be sorted by either calming mobs or simply killing them all, they respawn fast enough. And like other "bosses" (named mob, the one you only have to kill once) in this chain, Aberrant Chimera can't be calmed.
Once you're done, just return to Stephen for your just reward and next sighting.
The Lament of Malah
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(3) are located at 2150x750 in Burning Marshes. Easiest way to reach them is simply traveling east, across bridge by Lord of the Void.
This time you need to kill 5 Desolate Malahas, 5 Grieving Malahas and 1 Embodiment of Sorrow. Upon completing, The Song of Sorrow will appear in your inventory.
This you bring back to Stephen. If you pull next quest, he'll also hand you Amplification Unit.
Facing the Shadows
This part of quest chain is biggest bottleneck. You're send out to kill
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(4) and loot Smoldering Hair Strand. They are located around 1000x1200 in Burning Marshes (Note: Half of inferno is named Burning Marshes. This particular spot is bit west of Petrified Hecklers). Unfortunately only 3 Smouldering Shadows spawn on random timer and Hair Strand don't have 100% dropchance. Once you're lucky enough to get one it's back-to-tourguide-time.
This is only quest that will update to map. It can be bit confusing, because while it shows on mini-map as dungeon, all the mobs are outside, located around 660x750 in Burning Marshes.
Now you need to kill 5 Feral Vortexoid Strikers, 5 Feral Vortexoid Soothers and 1
(6), this time Ember ones. You need to loot Ember Chimera Tooth. Unfortunately they don't give up on their teeth that easily and more likely than not, they have Broken Chimera Tooth (wrong item). They can be found on path leading to Vortexoid mobs and behind their camp, approximately 520x750 in Burning Marshes. Should you secure one, return to Stephen with it.
Prize Hide Hunt
This quest will reward you more than usual 1 mill, you'll get 500k credits more. Guide sends you out to retrieve Coal Lizard Skin and Smoky Salamander Skin. You'll find both types of mobs around pond at base of Drop-off Point, Salamanders(7) usually populate more northern area while Lizards(7) lurk down south to scare newcomers. Neither mob has 100% dropchance and not to spoil everything, I won't list which mob drops which hide.
Reward for this quest is profession specific. If your profession isn't named, you'll walk off with only credits. Traders, with their ability to haggle, get Mudurlurgu Acid Spitter, Engineers get Acid Splash Special and Fixers Nano Crystal (Luck's Capricious Consequence). Last assignment come in pair since you're after two dragons with rather special loot.