This rather messes up cargo and passenger delivery schedules.

Today it seemed to me that it added 10 days to the date when the jump should have taken 10 hrs.
Unfortunately I only noticed after a series of events.
I jumped from Inbibe to Laribebi (G2).
Fought my way to the main station.
Sold some cargo I had found floating around the place.
Swapped my Arafura for an Imperial Courier.
At this point I found that:
1. 4 passengers and 3 out of 5 passenger berths had disappeared.
2. The date was 10+ days later
3. I still had the gold and gem stones I was due to deliver but the gold delivery date was past due.
I did not hack the save file, just redid the trip but did not buy a new ship.
The two previous cases did not occur in quite the same way. I did not buy a ship, I just suddenly found myself with "no time" to deliver about 5 high value cargoes. I had to fix that by editing the save file. That's not the way I like to play the game!