Dates of Service for monthly DME rental ???

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I'm billing for DME rental. I know to use modifier RR for rental. and KH, KI, and KJ for the consecutive months......but I'm not sure what to put for dates of service.
we gave the DME to pt. on 9/21/ I am sure that goes in the first "from" field.
but then do I just leave the "to" blank? or put 10/21/10.
then for the second I put 10/22/10 - 11/22/10
or do I put the last day of the month in the "to" field? like this...
first month as 9/21/10-9/30/2010
second month 10/1/10 -10/31/10