Yes, you can safely leave your car at DHS. Or drive to Epcot and leave the car in that lot and take the bus over to DHS from the front of Epcot...yes, there is a bus to DHS from there.
Then, after you check out the lights at DHS (which are incredible by the way!!..but very crowded) you can do one of two things...1. boat back to Epcot or 2. walk back to Epcot.
Which one to do?? Depends. If there is a boat at the dock, or coming in, then fine, hop on it. It may be very crowded though. But..if there is no boat in sight, or one is just pulling away, you may have a longish wait (up to 20 mins or so) until the next one comes in. Then, it's about 25 mins on the boat to Epcot.
The walk takes about 25 mins...depending on your walking speed. I have done it, with a stop in my room at BWV, in 18 mins, but I was cranking!! I would plan on about 25 mins. A friend and I left the boat dock at the International Gateway just as th boat was leaving....we reached BW at the same time, but we beat the boat to DHS by about 8 mins..we walked. The boat was just coming into view as we got to the bag check area. The walkway, along the canal, is very well lit and safe...a very nice walk, with plenty of others along the way.
Be aware though....both these times are from the front of the park...once you get outside the park. You will have to plan on another 10 mins or so to get from the lights area to the main gates..you'll be like a salmon swimming upstream!!
The nice thing about leaving your car at Epcot is that you can leisurely walk through Epcot after dinner.....shorter and nicer than walking back to DHS.
