Injury time - non old firm clubs

Is this set as a standard 3 mins for games not involving the old firm? Blew right on 45 first half and 3 mins never even covered the amount of subs. Dundee started slowing the game down about 65 mins onwards. Of course, looked like we could have played all night and not scored but guaranteed if that is one of the old firm would have been 6 mins minimum - and how many times do they score in that time.