Actually Saturdays the least favourite day for most people to want to work, so it's possible. Numerous people at my store are down for 8 hours on the schedule, so not sure how they do it, but working under 12 hours is possible.
But you'd already be down for shiftss over the next 3 weeks, so you might no be helping yourself there, if you knew this way in advance, they'd probably be more helpful. I dunno, it really comes down to budget issues too, being the start of a new tax year...a lot of stores love to get unpaid leave in and stuff to get their targets down to allow more freedom around busier periods.
Another random question.....we use the self service tills on nights sometimes at our store, so obviously when the stores closer, except for sundays....but I bought something at 5 as I was leaving and someone who works admin told me I shouldn't have just as it went through....seems a weird conflict there, is the person opening it at night in the wrong? Or is the guy in the morning just being fussy?