Nord to Montparnasse question

Hi all!

I’m starting to poke around more seriously trying to figure out my trip from London to SJPDP. I won’t have the jet lag issue since I’m arriving in London on April 17th (a.m.) and looking to start heading to SJPDP on April 19th.

I am leaning towards the train because I have a serious soft spot for trains and not to mention the other time I’ve done the Paris to Southwest France train trip, I did it at night so I want to do it during the day this time.

I know I can't book until 90 days before leaving but I did manage to find the hours of the trip I'd probably like to take. Depart London at 7:55am (St Pancras) and arrive at Paris Nord at 11:26am. Apparently, I’m to somehow make it from Nord to Montparnasse in an hour as the TGV train leaves at 12:27pm. Has anyone done the trip from Gare Nord to Gare Montparnasse? I did check around online and some seem to say it is a 15 minute metro trip and others say it is over an hour metro trip! So I’m confused Anyone has experience on this?

The rest of the trip is straightforward: arrive in Bayonne at 5:32pm, depart on a TER train at 6:07pm arriving in SJPDP at 7:33. My idea would be to then find a place to sleep (or pre-book), find dinner, sleep, next morning wander the town and have lunch. Then about 1pm, make the trek to Orisson, where I have a booking for the night.

Thanks!
-T

Thanks, for your responses Joe and Kitsambler! I’m laughing because your two response are exactly what I’m finding online – some say an hour and others say 10-15 minutes! What I’m now thinking of doing, to avoid this whole Nord-Montparnasse thing is leave a couple days earlier and travel through Toulouse and reconnect with that lovely city (was there for 5 months in 2006).

Thanks for your input!
-T