Kevin Garnett -- Timberwolves Fans Jump Gun ... Buy Tix to Wrong Game

A bunch of Minnesota Timberwolves fans are trying to exchange their tickets to tonight's game -- after learning Kevin Garnett won't make his re-debut with the team until Wednesday ... TMZ Sports has learned.

Of course, Timberfans went CRAZY Thursday ... when it was announced the future Hall of Famer was returning to the team that drafted him in 1995.

The box office went crazy -- with people trying to buy tickets to KG's first game back ... many of whom assumed Friday would be the night.

But the team announced Garnett won't hit the hardwood 'til Wednesday ... and box office sources tell us, "There were a lot of people who bought tickets for tonight's game because they thought it'd be KG's first game back. Now they're all calling, trying to exchange the tickets for Wednesday's game."

Unclear how the team plans to handle the situation -- but a team rep tells us they're excited for Kevin's return ... especially since Timberwolves home attendance is the worst in the NBA.