Honestly... I have no idea. But I would expect it'll take some time since the rate of healing depends on the amount of magic Niti currently has and just how badly injured Jeanne is. Although he's skilled at healing, his magic is running low since it went to that barrier. Jeanne did nuked herself... How much damage did she take? 

Also, thanks! I'm not very good at describing things in a pretty way, but I'm working on that.