We have stopover for 8 hours on way to malaga. Are we allowed to leave airport and go into dublin, if so what is quickest way to dubljn city centre and temple bar. Is st. Stephens green in walking distance to temple bar? Thank you

Assuming you carry a passport from a visa-free country, yes, you can leave the airport.

Several bus options -- the Dublin Express to Temple Bar takes approx 35 minutes. Are you able to check your bags through? If not you'll have to build in time to drop your bags and pick them up at Left Luggage. You'll probably have to do that anyway for your carry-ons.

Do I have to clear customs in Dublin if I am flying from canada to malaga with the 8 hr stop over? How long does it take to clear customs?

I think you probably mean Immigration/Passport Control and the answer is yes. How long it takes depends on how many international flights had landed before yours, how many agents are working, etc. Customs is a formality but you will pass that, too. It's typically non-existent assuming you have nothing to declare (as in goods).

And you will have to go through security again. If you leave your luggage at airport (as in hand luggage), you will have to go through security when you return for your final flight.