1. A method for generating time-horizons for long term orbit models for at least one satellite within a global navigation satellite system (GNSS) comprising: computing a predicted orbit parameter in an orbit parameter prediction model; producing an indicia of accuracy by comparing the predicted orbit parameter to a current orbit parameter; if the indicia of accuracy indicates at least a predefined level of accuracy, setting a time-horizon for the orbit parameter prediction model at a first value; and if the indicia of accuracy indicates less than the predefined level of accuracy, setting the time-horizon for the orbit parameter prediction model at a second value, where the second value is less than the first value.