Anything at global scope in the file is run once per process. Anything in the function is run once per request.
If you have multiple processes, then each process has to load it even if defined at global scope, so if lazy loading (default) is used, then you will see that delay as part of the first request time against each process.
You can force preloading of the WSGI script file in the process by using the configuration:
WSGIDaemonProcess mytest user=apache group=apache display-name=me-mytest processes=5
WSGIScriptAlias /mytest /xxx/bin/mytest.wsgi process-group=mytest application-group=%{GLOBAL}
<Directory "/xxx/bin">
Require all granted
</Directory>
That is, set both process-group and application-group on WSGIScriptAlias.
That will trigger the WSGI script file being loaded when the processes first start and not lazily on first request.
Graham