Times for Paris metro from St.Lazare to Montparnasse

Avoid rush hours (or the times when public transportation is most used and tends to be crowded) in most major cities around the world are usually 7am-9am (going to work) and then 4-6 (going home from work).

What time does your train arrive to Gare Saint-Lazare? I'd think midday would be less traffic than rush hours but I'd also not want to hang around a train station.

I'd download the CityMapper app and at the time check to see which line (either 13 or 12) is running the fastest.

Thanks to Jazz/Travel and Pam.
I'll check City Mapper for travel times.

Ratp.fr shows the trip going from St. Lazare to Gaite on the train with an 8 minute walk on arrival -- and about 11 minutes on the train. -- they estimate the whole trip at 21 minutes. Of course, there is also the waiting for the next train, but trains are frequent. FWIW the 13 line which connects the two is one of the most crowded in Paris.

We arrived at Montparnasse at 2:pm last week and took metro 12 to Abbesse, not crowded at call.

I'd download the CityMapper app and at the time check to see which line (either 13 or 12) is running the fastest.

Do check for line 13 disruptions, but if there are none, take line 13: it stops much closer to the Montparnasse mainline train platforms than line 12. The difference is an almost 10-min walk.

And Paris rush hours are later than stated above: the worst times are more like 8:00-9:30 and 17:30-19:00

Thanks for all your helpful suggestions!