import datetime
total_time = datetime.timedelta()
lst = ["00:33:33", "00:23:34", "01:32:21"]
for time in lst:
hours, minutes, seconds = time.split(":")
hours, minutes, seconds = int(hours), int(minutes), int(seconds)
total_time += datetime.timedelta(hours=hours, minutes=minutes, seconds=seconds)
print(total_time)