I'm a back-up food and beverage controller for a restaurant that gets live maine lobsters several times a week. During dinner we have a visual presentation to each of our guests including the lobsters. This is at room temperature., so keeping lobsters alive is very important.
Your situation sounds tricky since you will be stopping to see the sights instead of driving right back.
Lobsters can stay alive outside water for a long time given that their gills are damp and varies on the quality of the lobster. Our lobsters are delivered to us in heavy duty waxed cardboard with frozen gel packs inside with the lobsters covered in pages of wet newspapers (free alt news weeklies
). With a tank they will last a long time - it's been so long since we had one - I'd say a week. In a refrigerator, covered as discussed above with damp cloths or paper, I'd give them a three days at most. They might give you weak lobsters and find them dying intimidately.
When your lobster stops swearing at you, stops moving, and its tail starts to separate (you see the blue squishy muscle in between tail and body) you know your has passed. I would recommend blanching the lobster before freezing it. I don't recommend eating lobsters that have been long dead - dead lobsters kill other lobsters in the tank and can't be good for you.
I hope this helps. If you have any more questions, just ask.