Gare Montparnasse-walk time on ticket

I'm not familiar with the SNCF site, but it might be counting the long walk from the Montparnasse-Bienvienue Metro station to the appropriate track in the railroad station. The Metro station is well north of the railroad station, I remember a moving sidewalk between them. But if you looked for a schedule that starts at Gare Montparnasse I'd have thought your journey time would begin when your train actually leaves, not when you start walking to it from somewhere else.

Of course there is a walk from the ticket machines and windows to the tracks, but I don't see how it could take anyone 14 minutes.

Try the d bahn website and see what you get. You don't need to buy these tickets in advance, it's a walk-up fare.

If you somehow selected the Montparnasse metro/RER station, or were connecting from elsewhere, then it could include walk time into the main train station. It does generally just take an hour (or sometimes 1h 16m) for the train ride itself. If something else was different, like the walk was re-directing you to a bus outside, that should be spelled out. It's a large station; see maps at https://www.gares-sncf.com/fr/gare/frpmo/paris-montparnasse/plan-de-la-gare.

Is that train leaving from Montparnasse Vaugirard? That is a side station with the platforms set back from the main station platforms about 260 meters.

I think Sam has it right - there are two separate groups of platforms at Montparnasse that are quite far apart, so the website may be assuming that you are starting from the other one to the one the train to Chartres uses.

https://parisbytrain.com/gare-montparnasse-photo-tour/

This blog is often useful because it illustrates main Paris train stations with photo guides. My experience with SNCF advice is that the time estimate applies to passengers who know where they are going. I take longer because I have to be careful about reading the direction signs. But not vastly longer; you know your own capacity best. The 260 metres is about 280 yards but the route involves changing floors. Crowds at the escalators could slow down the impulse to sprint.

Thanks everyone for your replies, it all helps.
When I did the same date/times on the voyages-snf.com site for buying tickets, it did not include this "extra" time.
I have also reviewed https://parisbytrain.com/gare-montparnasse-photo-tour/ and found it very helpful.
In reviewing their /paris-train-ticket-machine page, under the 2nd picture, in the payment discussion, it says "North American & non-smart chip credit cards will most likely not work at ticket machines NOR AT TICKET WINDOWS-ONLY CASH". I knew about NA cards not working on their machines but I thought that the benefit of Ticket Windows is that they WILL accept our non-chip cards.
So does Paris' Train and/or Metro ticket windows accept non-chipped NA credit cards for payment? At all of the major train stations?
Thanks

So does Paris' Train and/or Metro ticket windows accept non-chipped NA credit cards for payment? At all of the major train stations?

I believe that Canada has been much more aggressive in adopting EMV or PIN & chip credit cards that has the USA so I am not embracing your NA characterization.

Still, any service window, sales or information, can process payments with a credit card, any credit card be it chip & PIN, chip & signature, or magnetic strip only. Information window agents will typically direct anyone with a chipped credit card to the ticket kiosks but if you only have a striped card, they can help you.

Thanks for the information.
No slight to Canada intended. The "NA" reference was made by the site I was references not me.
Thanks, Fran