Theres a lot of debate as to whether or not routine worming is necersary but IMO, I would do a 28 day course of Panacur when accuiring a new bunny or prior to bonding/boarding as that will hopefully eliminate any nasties that could be in the gut.
I do tend to do a full course of Panacur once a year on our two as a 'treatment' course rather than a preventative measure even though it is for prevention as hopefully there is nothing worm wise going on but the 9 days of Panacur does not treat for EC which is why it is not very effective.