thumbnail server: add leader to time offset, when present
thumbnail server: add leader to time offset, when present

CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator,CMU-CREATE-Lab/timemachine-creator