welcome to our community and thank you for sharing the questions with us.
As for your questions:
1. He can apply at any point for asylum, omce he applies for asylum he looses the visa and the rights that comes with that.
2. Whether he should submit his passport or not cannot be answered by us as we do not know the exact the situation he hisfleeing from in Afghanistan, but in general you are legally oblied to submit your identity documents if you have them. If not at the start of the procedure then at later stage.
3. No even if he submits his passport they will have to process his claim and check if his claim is rightful and he should be granted protection or not.
4. Usually when he applies they first register his claim and only couple of days later he gets an interview but this differs from BAMF brach to BAMF branch.
I hope we could assist you, if you have further queston please feel free to use the platform.