
If it's Panacur 10% then you start at day 14 as it instructs on the box. I Panacur my bitches during pregnancy, and do the 3 day course for pups at 2 weeks, 5 weeks and 8 weeks. Again at 11 weeks if they're staying.
At 2 weeks and 5 weeks I Panacur Mum, but not for 3 days. And not at the pregnancy dose. You just do her for one day only, at the normal adult rate. Have done this for years.
It's the manufacturers recommendation, and it has been problem free on my toy breeds. Wouldn't use anything else, because I have no reason to.
At 17 days I would be getting their first dosing right away.