In principle you have to expect a months time before full weight bearing But it always depends on the sort of fracture and how well it is "aligned". The fractures tend to heal fast and well. But keep in mind that final results are depending on the rehab. To let yourself and your patient be guided by "pain" is a good idea. Realise though that there are different sorts of pain (e.g.sharp/throbbing) which handles different sorts of information about what is happening at the fracture site. Increase of pain over time should be a red light as you can understand.
The problem though is you are having a sporty person who likes his running (otherwise he wouldn't run, to boring) so you have to hold him back otherwise in years to come he will be less greatful.
Cheers