You can evaluate cards in Kaiten how you like: in hours, in story points, in dollars and etc.
Open the card, click on the purple button in the upper left corner and select "Size". After that, the "Size" field will appear in the card.
Then click on the Set Size link and enter the value. Click "Save"
Open the card, click on the current value in the "Size" field. In the window that opens, you can change the estimate of the size of the task or delete it.