Hi Adam
I was in much the same position during my PPL training. I'd book 2 1 1/2 hour slots every other Saturday with at least a one slot break. Some weeks I would fly both slots, some weeks just one slot, rarely both slots would be weathered off. During the breaks I would talk to other pilots and instructors, ask about flight plans, even had a free ground school on radiation fog (one fog bound day) and if there was no one about I would sit out airside with the radio scanner listening to the RT. During training no time at the airfield need be wasted even if the weather is bad (there will be at least one bored instructor about to explain about flight plans, NOTAMs, TAFs, METARS, etc).
Regards Chris