How do I adjust cooking time for dense fruitcake in smaller pans

I'm making a fruit-laden very dense fruitcake. The original recipe is for 2 standard loaf pans but I'm using 4 small loaf pans (all I know is external dimensions are 6.875 x 3.625 x 2.125)

Recipe says 3 to 3 1/2 hours (check for toothpick comes out clean after 3 hours) @ 275 degrees.

I assume a smaller cake will cook in less time but other than checking all the time with a toothpick, I have no idea how long they will take.

Any suggestions greatly appreciated.