PSS convertion from Frequency to time domain
The PSS signal is generated based on Zadoff-Chu sequence and is mapped to the central 62 sub-carriers apart from DC sub-carrier as explained here. If you want to view the PSS alone, leaving aside other subcarriers in the PSS containing OFDM symbols then yes, you'll have to do a 64 IFFT on the length 63 Zadoff-Chu + DC symbols. It is worth nothing that on the receiver side, synchronization is achieved by locking on to the central 63 subcarriers using a 64 point FFT.