It depends on the settings you have configured but you do need to watch your descent profile, if it's not good FDC might think you are climbing again (maybe due to a missed approach) and then it won't lower the gear at all!
Thanks for all your support so far mate. Pf3 has my descent rates and they work well. What settings can we adjust as even at 500ft theyre not down and have to do them myself. Flaps etc are done by fdc no problems.