King Krush
First rare sighting, I saw him twice - once at lvl 77 and again at 80, but had no chance of taming him without heals or debuffs and with a valley full of players trying to kill him as well. No time looking, 2 random sightings.
Gondria
Spent about 6 weeks circling its spawn points for a couple-few hours a day. I figured there would be less competition than for Loque. When I finally saw it I panicked but pulled the tame off without much of a problem. My heart raced for a couple of hours. 40-60 hours?
LoqueI circled and camped spawn points for months, and mined the perimeter of SB all while on top of that, I'll bet 100 hours went into that search not even counting the time I spent mining and looking. I never saw a trace while I looked, NPCscan never went off. I gave up and went to look for Gondria instead, then one day I woke up early and was doing some mining when there it was. I was so excited that I dismounted in mid-air and almost killed myself, and I made pretty much every mistake you can make including being out of spec, having a pet to dismiss and having to feign once and wait for enough mana to build with nothing to drink. Thought for sure someone would come along and steal it but I somehow got it and I was buzzing for two days. I can't help checking the points when I go there for my oracle eggs and have tamed two more since after not seeing any hunters online. 100's of hrs no results., 3 random finds while not looking.
Skoll
Easy tame, parked at the supposed best spawn point above the village when he was first put in the game and he spawned right in front of me a couple of hours later. 2 hrs.
Arcturis
Same as Skoll, parked there early in the morning when he was new and he spawned right in front of me after just a couple of hours or so. 2 hrs.
Karoma
I REALLY wanted Karoma after trying and failing to get the spirit wolf and having such a half-hearted guild to help at the time. It burned every time I saw one. I leveled to 85 as fast as I could so I could camp before the rush. Easiest tame of them all. I was scouting the spawn points and landed to check out a potential point to camp and BAM, he spawned right in front of me in the middle of the afternoon. Less than an hour invested.
Sambas
I thought I'd get Sambas since I had extra time budgeted for Karoma, and it seemed that he was more in demand than Karoma on my server based in how many people were spamming and looking for him. I spent almost a full weekend camping after getting a tip about a spawn time. He finally came up after a 10 hour session of cruising the spawn points and working my mining skill up on the hillside. I really put a lot of continuous time into this one, usually I'd just spend a few hours at a time at the most. Probably 25 hrs total.
Ghostcrawler
I figured I may as well get them all. I scouted the area and learned his route from the map linked here the first night. After an hour or so of mining and loosely looking, I was ganked by a horde hunter while I was afk and about to log. He tried to shoo me away which prompted me to come back and start pulling out other spirit beasts to mess with his npcscan before logging for the night. He PMed me the next day on an alliance character to gloat about taming him right after he saw me and thanked me, thinking he drove me out of the zone - then told me how full of lose I was.

Terrorpene
I wanted a replacement for my turtle, he was right there for me the second time I checked his spawn point. 30 minutes.
Jadefang
The quest wasn't up for 4 days on our server and every time I was in the cave there he was in the cave, setting off my alarm. I figured it would be easy so when I finally got the quest I got up there and logged for the night, thinking he'd be there in the morning when I came on. Nope. I waited, and waited, and waited. Was over 14 hrs I recall before he spawned. I figured I'd stay for the companion and he was up when I woke up the next morning, like I expected the first time. 15 hrs straight through.
King Krush
Went back for he and Aotona after getting bored camping Maddexx. Found him after about an hour, very easy tame at 85 now.
Maddexx
I basically camped for two days straight while listening to football on the TV. Saw him once as I swung into the zone, turned around and poof - he was gone without a trace. I think there are phasing issues like we see with the mining nodes in that area. You hit one particular node for instance and 4 suddenly phase in around it. I flew back and forth for at least 20 hours on the weekend with no results before finally spotting the green one while checking early morning before work on Monday. App. 24 hours.
Aotona
Last one I really wanted. I went back to SB through the portal in Un Goro Monday evening after taming Madexx that morning, and Silverdragon went off right as I popped into the zone. I cruised the spawn points and there it was sitting there for me. Done. 3 hours invested counting time in between Madexx.
Ashtail
I thought why not, and he was there waiting for me when I got there. Travel time only.
One thing I notice is that being an early riser sure helps in this sport. No competition.