DF1
TimeStamp                     ID          Size
2018-07-12T03:34:54.228000Z   46236499    0.0013
2018-07-12T03:34:54.301000Z   46236500    0.01119422

DF2
TimeStamp                     Size         ID #new column
2018-07-12T03:34:54.292Z      0.00         blank #no match/no data
2018-07-12T03:34:54.300Z      0.01119422   46236500 #size and
                                                    #timestamp match within tolerances