Uncanny Avengers #16-17 any any indication, apparently not long, potentially making his healing ability as strong as Wolverine's healing factor.
In Uncanny Avengers #16-17, the Apocalypse Twins, Exitar the Celestial Executioner to destroy the Earth, leaving Kang with nothing left to try and conquer. Before that happens, the Twins face Captain America and Thor, and the God of Thunder goes toe to toe with one of the twins, Uriel. Thor is quite angered by their intended actions and their stealing of Jarnbjorn, the axe he enchanted with the ability to kill Celestials. Thor grabs Uriel, forcing him into a portal that exits directly into a sun, burning Uriel until he is nothing more than ash. As a result, Thor's arm is burned down to the bone from forcing the Apocalypse Twin in.
Related: How Did Thor Lose His Eye in Marvel Comics?
Thor then flies into space to do battle with the other twin Eimin and Exitar, and Thor faces them both with his arm severely damaged and burned. Tragically, Thor and the other heroes fail to stop the inevitable, with several of them dying and the Earth being destroyed by Exitar. Thor manages to escape to Asgard, where he speaks with his father. As they talk about the loss of Earth, fans can see that Thor's arm is already starting to heal, with muscle and skin starting to come back mere minutes after having been burned off.
This display of healing seen in Uncanny Avengers is not unlike the healing factor belonging to the X-Men's Wolverine, that would be another story and unlikely to grow back like Wolverine's would.
In any case, fans can rest easy knowing that Thor and the X-Men were able to reverse the events of the Earth's destruction at the hand of Exitar by projecting their minds into the past and changing it for the better, saving the day. Thor's arm also came back perfectly healthy and healed as well. Though not as strong as Wolverine's, it's interesting to know that Thor can heal most damage with a god-like speed.
