User blog comment:Shaw Fujikawa/Lontar, the Emissary of the Future/@comment-1642876-20121022191231/@comment-71.251.235.14-20121023173808

From the sounds of it, he comes back with as much health as he had at the point he rewinds to. So it would seem better to activate it earlier, but it might mean that you are closer to the enemy team if you were running from them. If you get hit by heavy burst, (i.e. Veigar or Leblanc) you will be able to fully recover instantly, which would be incredibly strong. If the damage is sustained though, you come back with less health because you can only rewind a few secnds.

I have a question of my own... If he revives with his ult, are the killers denied the first set of gold from killing him? Or can they get the gold from killing him twice?