Is Windsor Castle, Hampton Court Palace and Kew Gardens too much for one day? About how long should I schedule at each location? I'm assuming I can take the train from London to these places. Is it possible to get tickets ahead of time to avoid lines?
I would suggest taking the train out to Windsor in the morning spend the morning in Windsor then the the train to Hampton Court for the afternoon. Visit Kew Gardens another day, you can take the District Line (underground) to the Kew Gardens stop, it's on the south bank of the Thames.
Use the Transport for London journey planner to help sort out your travel arrangements
http://journeyplanner.tfl.gov.uk/user/XSLT_TRIP_REQUEST2?language=en
Use "Windsor Castle" and "Hampton Court Palace" as your named destinations and "place of interest".
And don't forget your two - for - one entry tickets to HCP.
How long you dwadle in each place is up to you. I couldn't start to do either one justice in three hours and all I've had to do is wander in from the car park. All three in one day would be really mean and you'd miss too much.
I'm unable to comment on the time for travel by public means.
I could never do all three of these in one day. For the first two I'd me worrying about having to catch a train and for the last I'd be worrying about closing time.
I agree with the others. You will save yourself a lot of time if you get there 15min before opening times. You are at the head of what turns into very long lines over time. There are so many great things going on at Hampton Court (demonstrations, tours, etc), you would miss all of that if you can only spend an hour or 2 there. Windsor has great walking tours outside the castle....and the town is interesting..Kew also has tours and is large.
If you try to see more than one, I think most of your time will be involved with transport and standing in line vs seeing great things.
If you still want to see more than one...be sure to check transportation connections and timing to see if it's even possible.
If I were you, I would assume I would be back some day, and focus on quality over quantity.
My parents did both Windsor Castle and Hampton Court as a single day trip on a bus tour. In their case they only saw the Hampton Court gardens and did not go inside. A bus tour also can drive direct from location to location, whilst for train travel the transferring between lines and resultant waiting eats up time. So all three in a day is too much. Even the tour buses don't seem to do it.
It'd be a shame to not do the tour inside hampton palace and tour the gardens at a leisurely pace. Even Windsor and hampton alone is cramming a bit.