soccer referee shirts

I was watching an international match a few hours ago. There was a substitution to be made and the assistant referee did not let the substitute player in until he tugged his shirt inside the shorts (he untugged it the moment he entered the pitch). Is there a rule regarding that?

Also in another match I watched few months ago, the goalie wanted to do something so he told the referee and ran outside the pitch and the game stopped for like 5 minutes (apparently he went 4 usin the toilet) Is that time added to the injury time in the end of the game? Just curious