Baking time for a 4 inch last-minute Christmas Cake

As a result of ill-health I am very late in baking my Christmas cakes this year. Since most of my relatives look forward to my efforts each year, I don't want to disappoint them so intend doing Delia's last minute cakes. However, I only want to bake 4 inch rather than 8 inch cakes. Could you please advise me how long I'd need to bake them.

Thanks

Diane