Thank you, Jakob. Yes it is reasonable that times have a date since, as you say, it represents a point in time and without a date it reduces to a point within any random day. So I’ve better include the date in the timestamps. The problem around midnight seems pretty straightforward to take care of.
Thanks to both of you for setting it straight for me.
As a side note: Regarding the GPS format, it is a bit strange but the NMEA-0183 standard actually do not use dates in general, only UTC time. E.g. the G+GGA and G+GNS messages (containing the lat/long-info I’m using) only specifies UTC formatted as hhmmss.ss which is pretty strange. In order to get the satellite’s date, I have to use e.g G+ZDA. No big deal, but as my application is keeping track of what my motorcycle (and myself) is doing on the racetrack, I sample the GPS at as high rate as possible (here 10HZ) and doing a lot of math on signals from other sensors like accelerometers, magnetometers, RTK and others to gain high precision also at speeds above 250km/h. So I’m trying to reduce the amount of data as much as possible.