Unfortunately, it seems there will not be a mascaret (tidal bore) to view during the tour until the 27th at 6:31 am, and a weak one at that.
I expect the tour will already be wending its way back to le Havre by then. If you think that you might still be interested, you can PM me, and I can supply the directions to some of the best places to view it.
Off to dig up some pics to whet your appetite now.