I've the need to display bimonthly clock tables, I was able to add this pretty easy in case the project would find it useful

--- org-clock.el	2020-03-12 06:52:14.000000000 -0400
+++ /Users/chopps/org-clock.el	2020-03-12 06:51:43.000000000 -0400
@@ -2719,6 +2719,7 @@
           (pcase step
             (`day "Daily report: ")
             (`week "Weekly report starting on: ")
+            (`bimonth "Bi-Monthly report starting on: ")
             (`month "Monthly report starting on: ")
             (`year "Annual report starting on: ")
             (_ (user-error "Unknown `:step' specification: %S" step))))
@@ -2768,6 +2769,7 @@
                           (let ((offset (if (= dow week-start) 7
                                           (mod (- week-start dow) 7))))
                             (list 0 0 org-extend-today-until (+ d offset) m y)))
+                         (`bimonth (list 0 0 0 (if (< d 16) 16 1) (if (< d 16) m (1+ m)) y))
                          (`month (list 0 0 0 month-start (1+ m) y))
                          (`year (list 0 0 org-extend-today-until 1 1 (1+ y)))))))
              (table-begin (line-beginning-position 0))

Thanks,
Chris.