I did a quick check of different recording times and found most are between 60-70 minutes, although some were considerably longer or shorter. Gould's 1955 recording was under 40 minutes.
These timing variations are too great to be explained only by differences in tempi. Individual performers may take or skip the repetitions indicated in Bach's manuscript, add repetitions, or make other interpretive choices. Bach later made changes and corrections in a revised second edition of the variations, and also added an appendix of 14 canons. All these factors could affect the length.