Your call. And it does depend what time of year you go. But you will probably put yourself squarely into the most crowded time at DL. Here is what many people do: Show up 2-3 hours after DL opens its gates, wait in all of the ride lines when they are at their longest, stay thru the heat of the day, then leave when they get tired at 5-7PM.
If you want to get more from your trip, and have it be more relaxing, and you are going during a busier time, here is how to use other people's tendencies to your advantage:
1. Stay at a hotel very close to DL. Here is map of local hotels
http://www.geocities.com/ashpsyche/DisneylandLinkMap.html. We have stayed at several, but have converged on gettting a suite at the Best Western Park Place Inn right across the street from DL - a 5 minute walk to the DL gate. We have found even the Howard Johnson (nice hotel BTW) to be too far us - stayed there in 2003.
2. Get to the gates 20-30 minutes before the park opens with your tickets in hand.
3. All the ride lines are short - ride a whole bunch of rides during the first 2-3 hours.
4. Collect FastPasses and use them after the early morning.
5. Take a break back to your hotel at Noon-1PM - as you walk down Main Street on your way out you will be going in the opposite direction of all the late comers who are coming in to wait in long lines all afternoon.
6. If you have not eaten lunch, then do so. The worst time to eat lunch at DL is guess when? It is when everyone else wants to eat. If you want to eat lunch at DL, do it at 11:30 or snack until 1:30 and then eat lunch. We eat lunch in our room most days. The suite at BWPPI has a fridge and microwave. This saves time and money. We plan in a special lunch on some days - we did lunch at the Blue Bayou last August.
7. If it is warm, take a swim at the hotel to cool off. Then take a nap - adults included.
8. Work in dinner however seems best. Either outside the park or in, or make some plans on some days for special dinners.
9. Return to the parks at 6PM after your long break and long nap in an air-conditioned room. As you re-enter the park and walk up Main Street, you will be passing in the opposite direction all of those who stayed thru the heat of the day and are now tired and ready to call it quits. And guess what? The ride lines start to shorten. Stay as late as you or your group can make it. With a 3+ hour nap, my kids made it to 11PM every night, and sometimes midnight.
10. Then return to your hotel on foot. It is only 5-10 minutes away.
11. If you are going for several days, plan in "a sleep late" day and go to DCA that day. It does not open until at least 10AM.
11. If you want to do sit down lunches or dinners - we did some of those too - then plan them in. I am not saying you should go commando all day at the expense of eating a good meal. I am not saying you should go commando at all. I am just saying that if you plan meals selectively and creatively you can maximize your time at the parks - and probably be less tired than those who do DL in the "conventional" way.