We investigate the real-time formation of spiral structures in electron–positron momentum spectra generated by spatially homogeneous, time-dependent strong fields. Using a spin-resolved Bogoliubov-transformation framework in the instantaneous Dirac basis, we track both the instantaneous quasiparticle distribution and the transition amplitudes during pair creation. We show that spiral patterns in the transverse momentum plane originate from azimuthal phase accumulation and interference among multiphoton angular-momentum channels. For a single circularly polarized pulse, such spirals appear only transiently: after the pulse, the dominant transition component develops an approximately orthogonal angular relation between its real and imaginary parts, suppressing the angular modulation and leaving nearly isotropic multiphoton rings. For counter-rotating circularly polarized pulses with finite delay, the two pulses imprint opposite azimuthal phases and generate delay-dependent interference between angular-momentum channels with opposite winding. This interference produces multi-arm spiral structures in the final spectrum; in the parameters studied here, a ten-arm spiral arises from angular-frequency doubling of a five-cycle oscillation in the complex transition amplitude. The arm number and orientation are governed by the relevant multiphoton channels, field helicity, and delay-induced phases. These results identify spiral momentum spectra as signatures of angular-momentum-channel interference in strong-field pair production.