Harp music is such a magical sound and can create a lovely atmosphere. Each wedding is personal but the following information will give you some idea of when it is usual to have music played.
CHURCH SERVICE, CIVIL CEREMONY OR CIVIL PARTNERSHIP
From experience I generally find that guests enjoy harp music played for fifteen minutes or so while they arrive and settle down in the ceremony room or church. This is a great icebreaker and it can also help the groom to relax as he awaits his bride! Then I can play as the bride walks in, during the signing of the register and for the bride and groom to walk out to. I would be more than happy to help you chose the music for your ceremony.
Background music during the drinks reception creates a wonderful ambiance. During the summer months outside drinks receptions can be catered for but I only play outside if a prior arrangement has been made. Harps are beautiful but expensive instruments and they do not like direct sunlight or changes in temperature. I am happy to play outside (weather permitting) as long as there is a flat solid surface and appropriate shading (not under a sap-dropping tree!) such as a big sun umbrella to protect the harp.
Background music throughout the wedding breakfast is a lovely accompaniment for your guests to relax to. Provided that there are no more than a few steps it is relatively easy for the harp to be moved between rooms.