Baby backs usually take 4-5 hours and spares take 5-6 hours in a smoker running at 225-250°F. A lot of folks here use the 3-2-1 method for ribs. 3 hours in smoke, then wrap in foil and add some of your spritz liquid to the foil pouch and cook for 2 hours, then remove from the foil and cook for 1 hour in smoke. All cooking/smoking at the above mentioned temps. If you are doing baby backs go 2-2-1 on the timing.
Hope this helps!
Take care, have fun, and do good!
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