Compile-time is anything that must be known prior to building the tree. I.e. anything referenced when _define_forest() is run --- number of antennas, for starters. These options go in the "TDL Options" menu.
Run-time is anything that's not needed when building the tree, but used once _test_forest() (or any other TDL job) is invoked. If you can change a variable and re-run a TDL job and that change takes effect, then the variable should be a run-time option. These go into the "TDL Exec" menu.