This is referred to in mission planning as Hybrid Local Solar Time (HLST). The time scales are uniform in the sense of mean solar time (they are actually mean time of some longitude), and are not adjusted as the rovers travel. (The rovers have traveled distances that make a few seconds difference to local solar time.)
Answer: An independent variable is exactly what it sounds like. It is a variable that stands alone and isn't changed by the other variables you are trying to measure. For example, someone's age might be an independent variable.
The independent variable is the variable that the researcher manipulates in the experiment. This variable will then be hypothesized in order to influence the dependent variable. The independent variable has a big effect on the entire experiment, and is very important in drawing the conclusion of the experiment.