It's technically feasible but it's a ton of rat race driving. Also why Blarney especially. Also Killarney ? Both are on Rick Steve's top ten tourist traps in all of Europe for really good cause.
Barney: Blarney Stone (Ireland): "Busloads line up to kiss a stone on the top of a castle rampart and get “the gift of gab.” The best thing about this lame sight is watching a cranky man lower lemming-like tourists over the edge, belly up and head back, to kiss the stone while an automated camera snaps a photo — which will be available for purchase back at the parking lot. After a day of tour groups mindlessly climbing up here to perform this ritual, the stone is slathered with spit and lipstick."
Killarney (Ireland): "This is a place where most tourists wear nametags — a traffic jam of tour buses. If you have the misfortune to spend the night in Killarney, you’ll understand what I mean. The town is a sprawling line of green Holiday Inns and outlet malls littered with pushy shoppers looking for plastic shamrocks."
There are spectacular things to do that actually have something to do with real Ireland very close. Great castles and sights in Kilkenny, a little over an hour or so from Cashel is the haunting, beautiful, incredible monastic ruins and lakes of Glendalough. There's also a ton of great things to do just outside of Killarney and you could stay in a great real Irish town with plenty of pubs, restaurants, trad music and sights like Kenmare, Kilorglin or Castlemaine and have access to all the good stuff and avoid the tour bus overrun, plastic lephrachauny Killarney. Instead of Blarney or Killarney you could spend the time at the Gap of Dunloe, Ladies View, Muckross House, Ballagh Beama Pass, Kinsale Sheep Farm, the Black Valley......or explore the insanely beautiful south side of the Ring of Kerry or the stunning Beara Peninsula.
Your day is too much driving, too hectic and honestly goes to places FAR surpassed in real Irish culture, real history, experience and beauty by numerous other spots. It's like skipping Yellowstone the Grand Canyon and a beautiful fun cultural spot like Taos NM to spend time at a 2nd rate water park and a big mall.
Honestly not trying to be negative but Ireland and its people are INCREDIBLE and you want to experience that not two of the very few spots in Ireland that are pretty poor.