On the Race Dashboard you will find a panel that will allow you to update the Time Formatting for this Race. 

Timing Precision lets you select from a few different options. This only updates the display of Reports.

Beneath the Timing Precision dropdown you will find the Rounding Rule setting, which will affect how times are rounded and therefore placements.

Finally, you will find the Leading Zeros option, which will let you pad your times with zeros in front, so that 1 hour 55 minutes and 58.12 seconds would read as 01:55:58.12 instead of 1:55:58.12