I am using pydub to mix two wav files in one file. Each wav file has about 25Mb and for me page is loaded in about 4 seconds ( so execution time would be 4 seconds ) 
Does this execution time depend on user's internet connection speed?  
If it has any sense : The test.py file is on GoDaddy Deluxe Linux Hosting)
No. The execution happens on the server and the execution time depends on the server specs and your script optimizations. The internet speed just affects when the client will receive the response after it is ready from the server and sent! 
So in few words: 

Server gets request from browser (time for request to reach server depends on internet speed of the client and the host) 
Server processes the request according to your code (Execution time depends on your code)
Server responds to client and client receives response (time for request to reach client depends on internet speed of the client and the host)
Does python script execution time depend on internet speed?