Recent spectropolarimetric surveys have revealed that 10% of massive stars host stable, large-scale, surface magnetic fields. The mechanisms that are producing these fields are unclear as of now, but their characteristics and overall impact on massive star astrophysics can be studied. Among the  magnetic subpopulation, NGC 1642-2 hosts the strongest magnetic field ever measured on an O-star (20 kG polar) which exceeds the others by a factor of 10. We measure a new rotational period for NGC 1642-2 after finding that the previously adopted 157.99 ± 0.94 d period does not effectively modulate periodically varying spectra and measurements from newer observations. We use Lomb Scargle and Phase Dispersion Minimization periodograms to analyze variations of spectral lines that were acquired with multiple spectroscopic and spectropolarimetric instruments. With new observations, we constrain the period within 153.96d and 152.47d. We find that our upper and lower measurements make a significant difference toward correcting the phasing of spectral lines and measurement. This rotational period window also helps to begin to resolve findings from prior UV, Xray, spectropolarimetric, and spectral analyses.