My "normal" profile would to be to slow down to 1st stage of flap limiting speed somewhere after the IAF and go 1st stage of flap. Then (assuming ILS here) half a dot before glideslope intercept gear down and power back to approach power setting (say 40% from 65% in a DA42) and pitch for GS (~5° nose down).
I think that the SP 1st stage of flap is about 110 kts, I certainly used to use 1 stage on an IAP @ 100kts.
NOTE: The "White Arc" doesn't indicate when the 1st stage of flap can be put in, but when ALL flap can be put in. Often the 1st stage can go in at a higher speed (i.e. above the white arc).