Lone Pine Lake is about 1,800' above the parking lot at Whitney Portal, and you have the milage. How long that will take you and your friend depends upon many factors, but for myself, I generally hike at a moderate rate of 1,000' per hour. The trail to LPL is broad with a moderate grade.
As to weather conditions - that's tough to predict. Right now we're having a week of unusually warm weather, but that's going to end tomorrow, and there's a small storm which may reach as far south as Whitney. There's a forecast for 3-6" of snow in the town of Mammoth, which is north of Lone Pine but approx. the same elevation as the Portal. It would be prudent to expect at least some snow on the trail. Also keep in mind there may be some snow on the road, which may or may not be plowed.
Watch this bulletin board and this one
http://www.whitneyportalstore.com/forum between now and your trip - between the two it will probably give you a good idea what to expect when you arrive.
Have a great trip.
