I used to sit reserve a lot in ONT when I was based there...but that was more than 10 years ago.
Back then, A reserve wasn't a problem driving from San Diego, however, B and C reserve could bite you in the butt with commuter traffic on the I-15 North.
My technique for C reserve was to drive up to North County with all my gear in my car, and sit at a Panera Bread place for a couple of hours, while I sipped coffee and surfed the internet. If I hadn't got a call by about 7pm, I'd drive home. If I did get called out from there, I'd have a huge jump on the commute up to ONT (and you'd need it during afternoon rush hour). YMMV.