Is a visit to Chillon Castle and Lavaux Vineyard in Vevey too much for one day?

I can only answer part of the question: 2 hours is enough time to visit Chillon Castle, and not every boat uses Chillon's landing so you might have to take the 201 bus back to Montreux - or really just take the train back to Vevey, since the most interesting stretch for the boat is between Ouchy and Vevey.

We saw the castle in the morning and then had lunch at a winery with spectacular views of the Lavaux Vineyards. There will be time for both. We did this as part of a corporate group which hired a bus to take us to the vineyards. I cannot give insight on transportation, but it may be good to book a winery tour ahead of time.

Hi Jen,
If you're an early riser and plan ahead some details it is a doable plan. If you take the train from Lausanne to Veytax-Chillon (train stop next to Chateau Chillon) around 8.30 in the morning you'll be done visiting the castle around 11 am. Regarding Lavaux, I suggest to go to the beautiful tiny typical Swiss village of St Saphorin (there are trains connecting the 2 places). The walled vineyards are superb and the views upon Lake Geneva and the Alps just spectacular. You'll also have a chance to taste the local wine and cheese right there in the village.
You can return to Vevey (also by train, just a few mins ride) and take a boat cruise from there to Ouchy. Check the CGN website to see at what hours the boats lve from Vevey. From what I remember seeing last year, there are quite a few cruises departing daily from Vevey to Ouchy.
If you need more help, feel free to message me. I live in Vevey :).

I second the recommendation for St Saphorin. Loved it!!!!

I’d skip Vevey. I much prefer the lakeside of Montreux. But I was there in June when all the flowers were in bloom.

I think you'll have plenty of time for Chillon, the winery and looking around in both Vevey and Montreux in a full day. I found both the trains and buses very easy to navigate around all three.