Paris to Bayeux

It does not sound like you are interested in Monet so go straight to Honfleur. Moreover the days get shorter in October if you are not interested in driving much when it is dark.
Also it is probably better to make the decision the day before based on the weather.

You're talking about a minimum of 5 hours driving. Not counting trying to navigate cities you don't know and find parking. Note that restaurants in France usually open for the evening meal after 6pm and it's not common to get a table, eat, and leave in less than an hour. It will be dark at 7pm in October.

I would suggest you pick one of the 2. You really don't have time for both if you want to tour the gardens AND do a walking tour. And given the sunset time of 7pm, I'd recommend being in Bayeux by then. Which would mean, if going to Honfleur, leaving Paris in early morning, driving there directly, having lunch, and then doing your walk about.

Maureen,
Driving websites always underestimate the time from one place to another. They don't take into consideration stops for gas, food and comfort, and for negotiating driving in towns and cities, finding parking, etc. Also the minimum times they give are on the autoroutes, not regular (usually more interesting) roads. KGC is closer about the travel time. You can do this if you leave Paris early and get into the gardens at Giverny first thing (maybe grab a small lunch there when leaving), and leave there by around 12:00-12:30. Then get into Honfleur by 2:00 or 2:30, do your walkabout, have dinner and stay there overnight. Having an early dinner will be difficult, plus driving on unfamiliar roads in a foreign country after dark wouldn't be fun. Leave for Bayeux early the next morning (just over an hours drive at best) and have almost the whole day there. Stay the night in Bayeux, then off to your next adventure.

And a word of caution. If you are arriving in France on, say, a Tuesday and leaving Thursday, you may still be adjusting to the time change, jet lag, etc. If you are considering your arrival day as your first full day and taking off the second day (arriving Tuesday, leaving Paris Wednesday) you most likely will not be in your best shape for the drive, especially if you are arriving on an overnight flight from the US. Don't forget to calculate these things in your plans. (We almost always drive in Europe, but hubby lived in France, speaks fluent French, and we are very comfortable with and experienced with French roads, road signs, toll stations etc. Don't underestimate the time it will take to acclimate yourselves to driving in France. It isn't hard, but does take some adjustment.)

Give yourselves time to enjoy wherever you stop. Bon Voyage!

P.S.
If you decide to drop something, I would ordinarily drop Honfleur, but since it will be October, Giverny will be closing down for the winter. The gardens' floral offerings will reflect the season, so may not fit the picture you are expecting. There will be fall flowers, though. Just a thought.

"but since it will be October, Giverny will be closing down for the winter."

The gardens are still pretty even at the end of October. I went last year on the day before or 2 days before they closed for the winter and there was plenty to see.

Where are you headed after Bayeux? Can you pick up one on the way back to Paris?

My wife and I drove from CDG to Giverny to Bayeux last September. Be careful, a few weeks after i returned home i received not 1 but 2 speeding tickets from this leg of our trip. By the time the notice arrived (all in French, without website i could find to translate), the fine had already escalated. An unpleasant memento to be sure.