I record flight times to the nearest minute but then round them to decimals (6 minute chunks, not that hard to do) for the hours columns. That way if the CAA wanted to go through it and work out the actual precise hours they would be welcome, but otherwise if they are prepared to trust my rounding it makes the maths easier.
Confusing sometimes as I record exact minutes in UTC but our club likes times on the tech log rounded to 5 minute chunks in Local. Sometimes I get that one wrong...
Tim