Actually to be pedantic, a day can mean many things from 86400 seconds, to the consecutive period of time during which the Sun is above the horizon, the span of time it takes for the Earth to make one entire rotation and is actually 4 minutes less than 24 hrs. So do the rules mean the last 24 hrs or 23 h 56 mins?!
If you were flying at 23h 58 mins, could you be prosecuted
Rules are rules, and this rule is quite simple to follow, and even I have a complete understanding of it. I am not convinced though, that this rule as it stands, is the most beneficial to flight safety. I'd much rather it was worded:
Blah blah..."either solo, with a flight instructor or with another safety pilot who is qualified and current on type". No additional passengers may be carried.
Co-pilot (P2) time can only be logged on "aircraft on which more than one pilot is required under the type certification of the aircraft".
This can be ambiguous too. You can get Single pilot ops, where the aeroplane is operated by one pilot, or the operation can be a two pilot op with both captain and co-pilot onboard the same aeroplane.