Yes. You can set the Smallest Time Increment for time entries in the Global Settings > Time and Expenses screen to zero (0). By default, this option automatically adjusts the billable/client hours and actual hours to the next time increment. The default minimum time increment is 15 minutes. So if you log time for 1 minute, Core will increase that and log it as 15 minutes. If you do not want any rounding of time, then set it as 0:00.