Can recommend a good practice in Calais - this is 'Centre Veterinaire Curie, 139 Bvd Curie, 62100 Calais - tel: 03 21 82 15 11'.
It is obviously personal choice - there are vets practices all over France that are now very familiar with the UK travel scheme requirements, so you will easily find one in Limoges. (The Defra PETS website has a link to the French Yellow Pages - in English!)From my own experiences we find it better to return to the area nearer to the ferry and get the treatment done here, as (you already appreciate) there is a very specific 'window of travel' being between 24 and 48 hrs after treatment. Early on in the Pet Travel Scheme Calais vets were the most aware too! The practice above offers an easy 'walk in' service, with no appt necessary. THey are very friendly, and speak some English. Be aware that they do close for a long lunch hour, and also its 'cash only', no cards etc! it should cost about 60 euros per dog. A Calais stopover is quite a good idea I think to do a bit of last minute shopping, you are spoilt for choice with hypermarkets (recommend Auchan on Rue de Sangatte, rather than the pricey Carrefour at Cite Europe), or if you don't like shopping drive to the 'Site de Deux Caps' just outside Calais beyond Sangatte - this is the Cap Blanc Nez clifftop lookout, with excellent walking and a great view back to the white cliffs of Dover. Lots of free parking up there for a picnic etc.
Finally I would say have a great holiday with the dogs, loads of us are doing so and experiencing no problems whatsoever. The scheme is now quite straightforward, just read up before you go, take spare copies of everthing (for you all!) and you'll be fine. Enjoy! Richard.