My wife and I are in the early stages of planning a trip in April. We plan on leaving form NJ Friday night and coming back the following Sunday- which gives us about 8 days of travel. We want to see the Grand Canyon, Yellowstone, Yosemite, etc. Is this enough time to enjoy it? Where in the midwest should we fly to to make the most out of our trip? Thanks

Not nearly enough time. Plus, you'll still probably be in winter conditions at Yellowstone.

If it were me I'd fly into Sacramento, get a car and explore the Gold country (gorgeous in early spring); check out Yosemite to see if you can spend a day in the valley (snow might still be an issue in parts there too; ) then aim for the desert (over Tioga Pass if it's open) and Death Valley. If you go fast you might be able to make the Grand Canyon on the 6th day, then a day there and another day to either Phoenix or Las Vegas to lose the car and fly home.

Yellowstone would be such a long detour that there's really no way to include it along with the other places in eight days, especially in April.

< Is this enough time to enjoy it?>

No. You are going to 3 areas that are quite a distance from each other. Even if they were within easy driving distance of each other, much of Yellowstone will be under snow, and few roads will be open. Yosemite will also have a fair amount of snow and road closures.

I'd suggest, since you're in the early stages of trip planning, that you do a bit of research on weather conditions before even starting to think about an itinerary and airport to fly into. Arizona and Utah would be great places to visit, although some of the parks in Utah at higher elevations will have snow.

Might I also suggest that you pull out a large map of the U.S. and locate the areas you're interested in get a general sense of the mileage involved and major cities nearby. By the question about which airport to fly into in the midwest, I gather you're not familiar with these areas. Any airport in the midwest would still be quite a drive to where you want to go - you want to fly into somewhere like Phoenix, Las Vegas or something else in the west.

In April lots of mountain roads will still be closed in both the Yosemite and Yellowstone areas adding the the length of drives. You could fly to Fresno, do Yosemite, then fly to Phoenix for the Grand Canyon and then fly to Bozeman for Yellowstone, but doesn't sound very practical. That time of the year I think you're trying do too much.

I have done all three but on different trips. Just too much travel and with a week you will never be able to enjoy the sights adequately.
I suggest you fly to Phoenix rent a car and travel North to Flagstaff. You may want to stop over at Sedona for a couple of nights and explore and hike the Red Rock Canyon country. The south rim at Grand canyon should be OK in April barring but it can snow and raiun there even in April.
Also from Phoenix you can trvael to Tuscon to see the Saquaro cactus in in the Saquaro park. Going West from Phoenix you can drive into CA to Death Valley National Monument which should be accessible in April.