Time is one of the principal factors affecting soil formation, as it controls the extent to which natural processes convert soil-forming materials (SFMs) into media suitable for sustaining vegetation growth. This becomes especially important for land restoration projects where SFMs have to be used in the absence of soil material. This paper examines short-term soil development in a clay SFM used as a landfill restoration cap by characterizing SFMs on an operational site that were restored at different points in time. SFMs that had been in situ for ten years since restoration retained less water at near-saturation and had a greater degree of aggregation. Organic matter (OM) and microbial biomass contents also tended to be greater in older-restored SFMs. Vegetation type appeared to control nitrogen (N) and respiration, and the sowing of legumes may be especially important where SFMs are used as soil substitutes. The results suggest that soil development in the SFM was indeed controlled by time, especially when compared with recent allied studies examining the use of soil amendments at the same site. The enhancement of the biological status proceeded at a faster rate than structure improvement. Within a ten-year period of restoration, a soil material capable of supporting acceptable vegetation growth appeared to have developed on the site. Nevertheless, land restoration targets should be set with the important soil-forming factor of time in mind.