Praise be to Allaah.
The evening (al-masaa’) is a lengthy period, from after ‘asr prayer until ‘ishaa’ prayer – all of this period is called masaa’ (evening). It is the same whether one recites the dhikr at the beginning of this time or at the end, apart from those adhkaar which the reports specifically say should be recited at night, such as reciting Aayat al-Kursi at night. Adhkaar which should be recited specifically at night should be recited at night, and those which should be recited specifically during the day should be recited during the day. With regard to making them up if one forgets them, I hope that he will be rewarded for doing that.