Update time format

[yarukishi]

• Rounding: display "1d" instead of "24h"
• Permit non-consecutive time unit groupings, like "1d 30m"
• Don't display increments with zero in the second unit ("1m" instead of "1m 00s")
• Don't zero-pad the second unit ("1m 5s" instead of "1m 05s")

Note that zero-padding on the second unit was previously inconsistent. It was used for seconds and minutes but not for hours.

Based on a user bug report in Discord. I tested locally and saw various time unit combinations working.