Set markers (for driving for example)

I Punch in when i get into my Car. Alle customers have to pay for the time i Drive to them. In the invoice the driving time is a separate Position. At the Moment i have 2 customer entries for every customer. "customer xyz" and "Drivetime customer xyz" but it would be great If i could Set some timestamps or Something like This (with a comment )
This would also bei great If i Change the topic and Something like This.