Why do you estimate when using a kanban? You might look at an item and break it down for simplicity. You also might go in with a goal of 'one card per member per day' or something similar. But nothing should be fixed to an estimate. If something is delayed, it should show up stuck in a lane. Respond as needed.
Because work is deadline driven by whoever is paying the teams' salaries. If you can't accurately estimate when you can get it done, you break it down until you can you get replaced by someone who can.
