74HC4060 lower frequency limit
There is no lower frequency limit to the oscillator section of the CD4060.  The output of the 2-gate oscillator goes through a Schmitt trigger gate before clocking the first counter stage.  I checked several 74HC4060 datasheets, and none of them show the Schmitt symbol.  This does not mean that the Schmitt stage is not present; it might have been considered an internal detail.  I've never had a problem with either the CD or 74 parts in very low frequency operation, lower than for this thread.

Note:  While the chip has no lower freq limit by design, there is a practical limit when the timing capacitor leakage current approaches the magnitude of the charging current.