Hi,
The only instrument I've blown is a recorder and I'd think that would be alright. But a trumpet?
Your stomach wound will make more noise than your instrument if you upset it. The hidden wound on your bladder might be silently weeping.
The stomach wound is a good barometer for your condition, in my opinion. You might test it when it begins to look healed and take it from there. But I'd think around 3 months unless you can play gently.
All the best, Peter