If it can be sorted without a chest drain, then he could be back up and running quickly (though probably not under the advice of the doctors). Neither of my collapsed lungs have been able to be solved with the needle through the rib cage and blow it up option. If he has to go the chest drain route, it could be 3-7 days with a drain in.
As soon as it is out, you are off though. I raced about 3 days after my first one was out.
If this is something new to Miles, then unfortunately, he is now as greater risk of it happening again. If it is a pre existing issue, he should have had elective surgery to minimise the risks (I have had it done to put my risks back down in the very low end of things).
Anyway, I hope for the best. If it is drains etc. then he is in for some serious discomfort and non movement.
Good luck and go miles!