How can I access /sdcard/ when I connect to PC (MTP)
/sdcard and /Internal storage are same directory.  

As for why the file does not appear instantly is because of a bug in MTP mode as MTP cache is outdated until a phone reboot. If you do not wish to reboot the phone, 

Possible Workaround:


Settings &rarr; Application Manager &rarr; All Apps tab &rarr; Media Storage &rarr; Clear Data  
Install SD Scanner app &rarr; Open App &rarr;  Click on Start Rescan


Tested and Works on Android 5.0 Lollipop