1. After what time do bosses respawn? I was on Dromund Kaas waiting for The First ( wanted to see how he looks like
) for almost an hour but he didn't respawn. And I was at good location.
2. How can I create Ops group?
End game level 50 World Bosses have a respawn timer of 2 hours, while leveling bosses may have respawn timers from 4 hours to more.
You can create an ops group by creating a party first, then right click on your portrait, then go to "Group" and choose "Convert to Ops Group".
The minimum number of people required for most World Bosses is 8 geared and on the same level as the boss. Any more decreases the difficulty of the boss. Higher leveled players can solo many bosses.
The Nightmare Pilgrim is the exception. It takes 16 people geared for EC HM to beat. Any more than 16 people causes a wipe.