Metro transfer between trains in Paris--is there time?

Paris Metro timetable shows this is a 24 minute journey on the direct No 4 line. The longest I every waited on a Metro platform was 6 minutes. Allow 10 minutes of walking at Montparnasse because it can be a hike from the Metro platform to the rail platforms. I think you can make it comfortably.
See http://www.ratp.fr/itineraires/fr/ratp/resultat-detaille/start/Gare+Du+Nord+%28METRO%29%2C+Paris/end/Gare+Montparnasse+%28SNCF%29%2C+Paris/is_date_start/1/date/2013-01-11/time/10%3A30%3A00/route_type/plus_rapide

Thanks very much!

My only worry would be the time taken to buy a Metro ticket at Gare du Nord. The queues there for machines or the ticket counter can get very long. If you can state how you are getting to Lille it might be possible to buy a ticket in advance. If you are travelling to Lille from London by Eurostar, for instance, I believe it is possible to buy Paris Metro tickets in the departure lounge at St Pancras.

Confirm with TGV that the Metro ticket transfer is included with the thru Lille-Bayonne ticket.

Thank you both for the additional advice. I am indeed getting to Lille by Eurostar from St. Pancrans, and will look for the Metro tickets in the departure lounge. I managed to find a schedule that gives me a 2-hour break between the two Paris train stations, so I may get off the Metro for a breath of fresh air at Ile de la Cité--(on the #4 line, too), in which case I doubt an included Metro transfer would suffice for two rides. I'm glad for the chance to see a little more of Paris above-ground! Planning a trip is a bit of two-steps forward, one step back, adjust something every day...so thankful for the Internet and people's generosity with advice!

Annonn You're not actually taking the Brussels train from St Pancras to Lille just to change trains to get to Gare du Nord in Paris as a momentary stop en route to the Gare Montparnasse so you can shoot out of Paris?? You do know that you can take a train straight from London right into Gare du Nord without the sidetrip through Lille?

Nigel,
Yes, thanks, I do know that I could have bought a ticket straight into Paris. The reason I chose Lille is that I want to see as much of France by daylight as possible before arriving at my destination (actually St. Jean Pied de Port after Bayonne.) I figured I'd land at Heathrow and have time to get across the Channel and have a good night's sleep before enjoying the trip south. (Don't ask why I didn't just fly to Paris--it's a long story.) Thanks for the help! Annon.

If you're looking for dinner in Lille, I recommend the Brasserie Alcide in the oddly-named rue des Debris Saint Etienne...

Thank you, I'll try it!