Plan to drive from Dingell Peninsula to Trim. Mapquest says it's 195 miles and would take 4 hours; this will be in September. Is that accurate or will it take longer?

it will take longer

From where on the Peninsula?

From Dingle town it is about 235 miles and about 5.5 hours if all goes well, longer is possible.

From near Castlegregory so not as far away as Dingle town. It's nearer to Trallee Bay. Yes, I figured it would take longer!

Add 15% to http://www2.aaireland.ie/routes_beta/# or I prefer Google maps http://maps.google.ie/maps?hl=en&tab=wl as you can drag and change the route but again add 15%

Forgot to add that as a native I would go via Roscrea and Birr from the M7 to the M6 at Moate will take a non native at least 5 1/2 hours by any route.

From Castlegregory it is about 220 miles and a minimum of 5 hours. 5.5 to 6 is more likely

(I really like AA's route planner for the UK and Ireland - but whichever on-line calculator your use, I'd add %20-%50 to the drive times)

We drove from Dublin to Dingle and up to the Connemara. We quickly learned that drive times meant nothing because we kept on finding very good reasons to stop and spend some time in little tucked away places that weren't in any guidebooks.

I feared that we would tire of the driving, but it ended up being really, really lovely. Enjoy!

Oh, and the signage in Ireland is wonderful. We were only lost once, and that was our own fault. Compared to the states, it's very easy to navigate Ireland roads.