depends where you live but for (say) Newcastle you have to allow 45 minutes at least coming from say South Shields or Whitley Bay - even from the town centre the Metro is 24 minutes and runs every 12 - 15 minutes minutes so you have to allow at least 45 minutes
Leeds Bradford is a complete bugger to get to from C Leeds
Manchester is a train every 10 minutes max and around 20-30 minutes to get there
What? All passengers live in, and travel from/to, the city centre that the airport is named after?