The vast majority of climbers take a vehicle to the 5th station and climb up from there. It takes 5 to 6 hrs on average so a round trip from the 5th station will take 10 to 12hrs. ie. A very long day but definitely possible.
If you're really enthusiastic, you can start from the base, hike 5 to 6hrs to the 5th station, crash for the night, climb Mt. Fuji the following day and descend all the way to the base.
Oh, here's a pic I found :
Just imagine being stuck in this lineup for 5hrs. Rubbing shoulder to shoulder with all those Mont Bell-wearing sheep.
