Metric time
The main problem with metric time is in the units. The International System of Units has only come up with prefixes for 10 units exponentially in both the multiple and submultiple directions. The first three multiples would be viable for use within a metric time system; they are 101 (decasecond = 10 seconds), 102 (hectosecond = 100 seconds; 1.666 minutes) and 103 (kilosecond = 1 000 seconds; 16.666 minutes) respectively. However, the fourth value in the SI Units is 106 (megasecond = 1 000 000 seconds; 16 666.666 minutes; 277.777 hours; 11.574 days). Followed by 109 (gigasecond = 1 000 000 000 seconds; 16 666 666.666 minutes; 277 777.777 hours; 11 574.074 days; 31.689 years); a relatively nonviable unit with which to measure human time/life. To make this system of prefixes work for metric time, standard units and prefixes would have to be made for the 4th and 5th exponents to make metric time work for talking about the time of human life.  These would be: