Not sure about LV while in M-Co, but I imagine you probably can.
You will have opportunities before, during, and after flight school for LV. Before flight school - enroute to Pcola you can take leave. I always took LV over the Christmas holidays, and after flight school - again enroute to your new duty station. Whatever you do, ensure you always take your leave - you need it, and you rate it - no matter what your CO, XO or OpsO says.
AArider