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We propose an efficient channel estimation method based on time-domain maximum likelihood (TDML) algorithm for polarization-division-multiplexed coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with the conventional channel estimation approach, although with overhead reduction, TDML demonstrates similar system robustness against transmission impairments, such as optical noise, chromatic dispersion, and polarization-mode dispersion. More importantly, TDML demonstrates enhanced tolerance against laser phase noise. The theoretical analysis is validated by numerical simulation of quadrature-phase-shift-keying CO-OFDM system.