Time in cards on KanBan board

Why is it not possible to show time on a KanBan card but it is possible on a Agile card? Please could you transfer the possibility from the Agile cards to the Kanban Cards. There is plenty of room for this and it gives vital infomation to the developers (for example; I have an hour to do some extra work, we have about 40 issues wich one should I take? The developer now has to open every card to show what time is involved which could take up to 15 minutes to find one that could be handled. Now he loses 15 minutes of his precious time!)