The acquisition time depends on a number of factors, such as the sample itself, the desired spectral quality, and the Raman spectrometer being used.  However, typical modern Raman spectrometers can acquire good quality Raman spectra in a few seconds.

Raman mapping/imaging experiments, which acquire many thousands of spectra, take longer, and typically total acquisition times for these would be in the order of a few minutes through to several hours.  This would depend on the number of data points being acquired, in addition to the other factors mentioned above.