"Mario Second" differs from game to game and could be between 0.4 to 1 real world second. At least in some cases it was caused by technical specifications:
A timer's count is approximately 0.6 or 0.7 seconds (in Super Mario Bros., one in-game count lasts 0.4 seconds, which is 24 frames in 60Hz NTSC or 20 frames in 50Hz PAL, and in New Super Luigi U and the Super Mario Maker games, it lasts exactly one second). When the time limit decreases to below 100 counts, the "hurry up" jingle plays to warn that the player is running low on time and the level's music plays at a faster speed. In newer Mario games, starting with New Super Mario Bros. Wii, if Mario loses a life after hitting a Checkpoint Flag, the time limit will be reduced when he restarts the level from that point.
Source: Time Limit in Mariowiki.