Complex sentence: During his first seven years, he was engaged in magisterial and executive duties but his talents were soon recognized, and in 1889 he was appointed an assistant to Sir Robert Sandeman who at that time was opening up communications with Baluchistan, Waziristan, and the Punjab.
Split into simpler sentences: During his first seven years, he was engaged in magisterial and executive duties. By 1889 his talents were soon recognized, and he was appointed an assistant to Sir Robert Sandeman who was, at that time, opening up communications within the regions of Baluchistan, Waziristan, and the Punjab.