Let's compile the complete CDEF:
DEF:ds0=router1.rrd:AVERAGE
- CDEF:ds0modified=TIME,begintime,GE,TIME,endtime,LE,*,UNKN,ds0,IF
+ CDEF:ds0modified=TIME,begintime,GT,TIME,endtime,LE,*,ds0,UNKN,IF
This will return the value of ds0 if both comparisons return true. You
could also do it the other way around: