  We report the detection of several quasi-periodicities around 0.6--2.5 days
in the optical emission of the blazar S4 0954+658. The source was observed by
the Transiting Exoplanet Survey Satellite (TESS) in six sectors and it showed
these features in all but one of them, with a QPO of 1.52 days apparently
present in portions of four of them. We used the generalized Lomb-Scargle
periodogram method to search for significant signals and we confirmed them
using a weighted wavelet transform for time-frequency domain analyses. We
discuss several possible explanations for these rapid quasi-periodic variations
and suggest that an origin in the innermost part of the accretion disk is most
likely. Within this framework, we provide estimates for the mass of the black
hole at the core of this blazar.
