train transfer time in Paris

You'll arrive at G. Lyon and leave from G. St Lazare. They're about as far apart as any two stations in the city. Surface streets connecting the two go through some really congested areas. The actual metro ride between the two takes ten minutes, maybe fifteen. Fiinding the subway platform and waiting for the train might take another ten, maybe fifteen. Fidning the train to Bayeux and waiting for it might take another ten, maybe fifteen. If you know exactly what you're doing and hit eveything exactly right (and the train platforms are close to the metro area) you could probably do it in twenty.

Metro line 14 goes directly from Gare de Lyon to Saint-Lazare. Trains run about every 3-4 minutes. According to the Journey Planner on the RATP site, it will take 14 minutes to get below ground at Gare de Lyon, ride the train, and get above ground at Saint-Lazare. viamichelin.com gives a driving time of 20 minutes under ideal conditions. It's almost certain to take longer than that. And you'll have to wait in line to get a taxi. Take the Metro.

And the assumption is that you're not lugging a bunch of luggage...

Since Eileen has nudged this to the top again, I'll make my case a little more strongly. I'm conceited; I think I know my way around Paris as well as anybody (but Tim has wonked me in the past about a couple of routings I've never thought of). I would bet that I could do it in thirty minutes by metro, but I'd snoop around the day before just so I wouldn't make a single false step. And my luggage would be on my back. And I'be be alone without somebody to slow me down. I just might make it with no rehersal in the OP's time limit. But my StupidFactor would be a lot lower since I know what the signs look like, etc. I'd also be standing in the door of the front coach when it pulled into the station (with my luggage on my back and nobody slowing me down). My guts would be in a knot the whole time and there would be little old ladies and small children strewn in my wake, but I just might make it. But I wouldn't bet on it. All bets are off trying to drive it.

I like Ed's suggestion of working your way to the front of the train just before it arrives in Paris. At the very least, make sure you are the first people out the door of your carriage. He has given you fair warning about how you can lose time if you're not familiar with the Metro system. And you'll need to allow time to buy tickets. As both Ed and Eileen suggest, be sure to pack light.

I think the answer to the question is no, it is not enough time. Take the next train and give yourself some time.