Great thank you - and yes, we definitely want to incorporate a boat trip in Lucerne to Pilatus! We may swap that trip with our full day in Lucerne, dependent on weather.

I wasn't terribly successful in finding any shorter journey than 4 hours from Colmar to Grindelwald unfortunately. But, at least the journey will be scenic!

Lucerne is rather compact and a few hours roaming around could be enough and maybe take the classic boat trip Lucerne - Fluelen - taking train back.

>>>Good to know schedules change for second week of June <<<

2nd weekend, not week. That is when all the European schedules change. (June, Dec).

Frankly, I wouldn't spend all that time traveling from Lucerne to Venice for only one day. You are spending more travel time going to an out of way place than actual time in the place. Simply not time effective. At that time of year, you could go somewhere much closer such as Lake Como and take a train back to Paris.

You could also do the Venice to Paris overnight train (Thello ? Trains France-Italie - site officiel) to really save daylight travel time and have an extra day in Venice - I'd try to stay at least two full days.

We had investigated Lake Como, but from most of what I have read, you need more time there than what we have. On the other hand, we can get a pretty great sense of Venice in the amount of time we have. So, we figured for a few more hours traveling, we will end up feeling like we have "seen" more. Seems a bit backwards, I guess. I will not rule out the thought, though.

Also, we will investigate the sleeper train. Thank you for that information - it is a good thought!

Actually, I think the sleeper will shortchange our time in Paris. We plan to do an airbnb and they check-in is later in the day, so we like the idea of getting in the afternoon before so we have a place to store our bags. Thank you very much for the thought though! I feel OK about about a day and a half in Venice - more time anywhere would always be better of course

Colmar to Grindelwald takes 3 hr 45 on most connections. (www.bahn.de/en)- I said before 2.75 because I mistakingly put in Colmar to Lucerne.

Yes day and a half in Venice better than no Venice a'tal. Whet your appetite for future trips there.

" Actually, I think the sleeper will shortchange our time in Paris. We plan to do an airbnb and they check-in is later in the day, so we like the idea of getting in the afternoon before so we have a place to store our bags"

Almost all hotel receptions accept luggage of people who cannot check in yet (because the room is not yet ready).

LUCERNE - VENICE:
Direct Arth-Goldau (Lucerne) - Venice train:
Lucerne dp 9.18 - Arth-Goldau (same platform) dp 9.50 - Venice ar 15.40
Standard fare Arth-Goldau - Venice 126 CHF, discounted webfare 57 CHF

It would be much better to leave Lucerne the evening before, however, in order to have a bit more time at Venice, may be like this:
Lucerne dp 17.18 - Arth-Goldau dp 17.50 - Milan ar 20.35. Sleep at a hotel close to the railway station, Michelangelo, Duca d'Aosta, etc. Leave Milan the following morning at 8.15 and arrive at Venice at 10.40. Book a hotel close to the railway station (Stella Alpina, Dolomiti, Villa Rosa, etc.), otherwise you waste hrs of your precious time with local transport.

Count 5-6 hrs from city center to city center for your Venice - Paris flight.
IMO it's a waste of time. Take either the Thello overnight train Venice dp 20.17 - Paris L ar 9.55 (arrival at your hotel probably around 11.00) or take the train and sleep at Turin if you want to arrrive in Paris in the afternoon only, may be like this: Venice dp 19.50 - Torino PS ar 23.19, sleep there, dp 7.36 - Paris ar 13.24

airbnbs may not be open for luggage drop.

....but there are lockers and "man powered" luggage deposits in the big Paris railway stations (like Gare de Lyon)

this train comes intoi Bercy Station in Paris? no lockers have to take metro to gare de lyon - hassle but possible.

The Thello from Venezia SL arrives at Paris Gare de Lyon

Good -old trains I took once went to Bercy, really a prologination of Gare de Lyon.