Don't know about log-book time logging but some time ago I worked for a company that operated a flexi-time system based on 6 minute 'slots' (i.e. tenths of an hour). This led to the situation that happiness was clocking on at 08:59:59 (i.e. 08.9) and misery was clocking on at 09:00:01 (09.0), having lost a tenth of an hour over the couple of seconds.
It also led to odd conversations when you asked someone what time it was. They would always reply 'three point two' rather than 'quarter past three'.