If we're understanding your question correctly, and you're asking if you can travel from Las Vegas to Los Angeles and back, via bus, in a day, the answer is yes, but we wouldn't recommend it. If you simply want to know about bus routes between the two cities and are planning on spending more than a few hours in L.A., then there are several options, depending on your budget and schedule.
If you really want to get from Vegas to L.A. and back in a day, by bus, the only option we know of is the Greyhound. Buses depart regularly from the bus station downtown (on Main Street, next to the Plaza) but it's a long journey, so if you're planning on returning the same day and having any time at your destination city, you'd need to take one of the really early buses. One departs at midnight and gets you into Los Angeles at 5 a.m.; the next one leaves at 1:20 a.m. arrives at 7:45 a.m. Return-wise, you could catch the 6:30 p.m. and be back in Las Vegas at 12:35; the next one leaves at 10:45 p.m. and doesn't get you back until 4:15 the next morning. If you book the ticket online, you can currently purchase a return fare for $84.
That, as far as we know, is the only bus service that can conceivably take you from Las Vegas to L.A. and back in a day; if you were asking more generally about bus services between the two cities, there are a couple of other options we know of that will transport you faster and in considerably more comfort, but you'll need to stay overnight.
Vince Express has been in business for three years and operates a daily service in a fifteen-seater bus that leaves from the Gold Coast once a day and delivers you to Los Angeles five and a half hours later. The fare's $40 one-way or $75 for the round trip. Click the link for more details and pick-up/drop-off locations.
Another option is Starline Tours, which operates a daily service from L.A. (and Anaheim) to Las Vegas (the Imperial Palace, to be precise). The round-trip fare from L.A. is $120 dollars and your vehicle's a luxury coach that features complimentary snacks, beverages, movies, pillows, and blankets. The journey time is 5 hours and fifteen minutes.
Megabus, which is part of the Coach USA organization, briefly operated a service from L.A. to Las Vegas commencing in August, 2007, with limited seats available for just $1. However, the service was termiated in June the following year.
As you may have read in this column and elsewhere, there have been several plans posited for high-speed rail links between Las Vegas and California, of which the so-called "X Train" sounds the most plausible. Allegedly, this service will be up and running in time for New Year's 2011, but we're not holding our breath.
