If doing the Lions Head or Tuckerman routes from the east or the Ammonoosuc trail and Jewell Trails from the west, they are both very doable in a day. Some people will stretch them out to two days on these trails but if you are in decent enought shape, the time that Kimball said is realistic. The key (among several) is to keep an eye on the weather forecast on our page on the day of your hike and start early. Regardless of your start time, pack a headlamp or flashlight just in case though. There is no guaranteed rides down.
When it comes to the height thing, if it is a major issue, I would recommend an up and down on the Jewell Trail if only planning a one or two day trip. Most do the up the Ammonoosuc and down the Jewell but the Ammie can get pretty steep the further up you go and I have had friends take issue on the trail when they look back down. But the Jewell keeps you in a lower pitch most of the way up. The best is to look at a topo trail map (which I recommend buying before hiking up) and look at the pitches yourself. There are also plenty of online resources and books to help you choose your trail as well.
Staff Meteorologist/Night Observer, KMWN (Mt Washington Obs., NH)