Extract cell values from multiband rasters

Question

I have the following function and code snippet to extract cell values for multiple years, format it, and save to a list. Each raster has 365 bands — one for each day. A separate operation is performed on each flattened list pr_flt which contains daily cell values of XY for 1991-2015. The cursor contains XY coordinates for each cell. The following code works but it takes hours to finish due to the huge amount of data and possible use of lists instead of multidimensional arrays. I am wondering if there are any suggestions to reduce the runtime of the code, if possible.

import arcpy

def row_to_values(row):
    values = []
    for col in row:
        if isinstance(col, unicode) and col != u'f':
            # split and convert all entries to float
            values += (float(v) for v in col.split(','))
        else:
            values.append(col)
    return values


with arcpy.da.SearchCursor(fc, fields) as cursor:
    for idx, row in enumerate(cursor):
        pt_annual_lists = []
        pt_loc = str(row[0]) +  str(" ") + str(row[1])
        for y in xrange(1991,2016,1):
            pt_year_list = []
            result = arcpy.GetCellValue_management(in_raster = "D:/temp/ras" + str(y) + ".tiff", location_point = pt_loc, band_index="")
            cell_value = result.getOutput(0)
            pt_year_list.append(cell_value)
            cell_value = [s.replace('\\n', ',') for s in pt_year_list]            
            pt_annual_lists.append(row_to_values(cell_value)) 

        # flatten list of lists
        pr_str = [val for sublist in pt_annual_lists for val in sublist]
        pr_flt = [float(i) for i in pr_str]