Timing syncronisation using polyphase decimation filter
The phases of a  polyphase filter can be interpreted as a fractional delays. Consider your filter with $8\cdot 256$ taps in the up-sampled domain. In order to avoid aliasing the filter needs to be a low pass that doesn't allow any content above $1/256$ of the sample rate.

Since there is no energy above $1/256\cdot f_s$ in the transfer function you can actually down-sample the impulse response by a factor of $256$ without aliasing. That means that all phases have the same magnitude response in the down-sampled domain. The only difference between the phases is a linear phase that corresponds to a fractional delay. If phase $0$ has a delay of "$0$" samples, then phase $1$ will have a delay of $1/256$ samples etc. in the down sampled domain.