It's 24 hours for right and 36 hours for left. They're really hard to find. Only the people who killed it know the time, unless you're really lucky and find one. It's best if you pop in at different times everyday, it won't always be the same time.
Does it respawn after s/c or patches?[/quote]
Yes, every time there is a SC or Patch, the respawns get reset, so your best bet to find one is right when the SC ends, and 2nd best way is to keep track of when the SC ended and wait untill the 36 or 24 hour spawn time is met.