My 13 yo neutered tom cat has been bitten on his cheek. 
We noticed the flat raw area on Wednesday and it looked ok (there was no indication it was a deep wound though I know bites can be hard to spot), I said 'let's monitor this' and that's what I did - checked the area for pulpiness, heat, etc and kept an eye on him. He seemed absolutely fine until late friday night when I realised his cheek on that side had suddenly swollen. He was shaking his head every so often as it was clearly a bit strange feeling, but his ears were nice and cool and at that stage he was still eating avidly.
Saturday morning he looked like he had mumps! I'd already decided to call the vet as soon as possible Saturday and get an emergency appointment, so that's what we did and he was seen Sat morning. DH took him as I had to stay home with our younger son who has LDs and would not have been helpful to proceedings. He said the vet seemed quite 'junior' and went into a back room to ask for a second opinion, but then decided to send him home with antibiotic meds (liquid) and Loxicom which is anti-inflammatory (and counter-indicated for our cat as it's made him sick previously - DH didn't know this and it seems not to have come up on his record, or at least the vet didn't mention it...). She didn't, as far as I know, start him off with an antibiotic jab. She said the meds were instead of operating but thought it would clear up on meds. We are to call back 'after the weekend' if it's not improving.
Cat is not happy. He's not eating (licking jelly off his food, the odd Felix biscuit treat) and I don't know if he's drinking, so I'm worried about that. He's lying on the bed at the moment but clearly not feeling his best - he's getting some sleep though. Earlier, he was quite unsettled and yowling (to be fair this is his default!) and ended up in DS1s room and squatted under his chair and actually had a shit!! (DS was extremely resourceful, saw what was happening and promptly put a bit of cardboard under his bum to catch it.) Our cat has done this sort of behaviour with urine before (when he's had cystitis) but not poo. We were keeping him in because I'm concerned he's just a bit dopey at the moment (vet didn't say whether or not we should do and DH did not ask...) but after that, let him out for a little while just in case. He's back in and on our bed, oozing slightly from the scab (lymph not pus, unfortunately - I don't think it's coming out at all and the vet didn't do anything to drain it).
So I don't know what to do really. He's had his daily meds and we should trust they will kick in, but I'm getting a bit concerned about fluids. When do we start worrying about that if a cat isn't eating their wet food? Should I try using a med syringe to dribble a bit in? (He won't like it!) I'm certainly going to call the vet tomorrow first thing. He's not hot, he's not roaming around upset, he's resting - doesn't quite feel like an 'emergency' to call on Sunday.
Has anyone experienced similar with abscesses - how long did the meds take to kick in?