Yes it should be instant, so maybe either pump worn or a leak. Pump is in boot above o/s rear wheel arch and air pipes run to boot catch and into doors to operate catches. Lets hope its something simple! I have never heard of one failing, or a leak. Do the door pins drop down into doors completely when you lock it? If you have after market chrome door pins with domed tops you have to be careful not to screw them down too far as this causes the effect you are having, due to the door locks being prevented from locking properly. Good luck mate!