My wife fell hard on her left cheek from her bike last week.

wounds are healing good but I have couple of questions.

1.  antibiotics - any side effects? 

2.  hair-line fracture on her cheek.  how long does that take to heal.

3.  delayed concussion symptoms?  She is showing some sign of it.  How long does this last?

I looked it up on line for the answers and am now more confused. 

Her doctor just told her to rest but didn't say anything else.

Every drug has side effects, but once you start antibiotics you really should finish them. The side effects of antibiotics are exremely mild and rare I seem to recall, but it has been a while since I did any research on them.

Hairline fracture should take a few weeks to heal, but that will vary wildly based on age and general health so it is hard to say. The delayed concussion symptoms should clear up in a day or two based on my past experience.

Just resting is almost certainly the best idea for this list of problems. They will all clear up on their own.

Antibiotics rarely have side effects other than basic nausea, diarrhoea etc but it does vary according to kind and there are a couple that rarely have potentially serious side effects. Agree with Gnizmo as to finishing them unless side effects are causing significant problems.

Fracture: as above, weeks rather than days.

Delayed concussion would be odd but still possible. If it's just headaches then that may be due to the cheek injury (referred pain) or another more minor bump that she got that was overlooked due to the cheek. Anything more than MILD headaches and she should get checked out again. There is one condition that can occur days or weeks after a head injury which is very serious which would need to be ruled out BUT it is EXTREMELY unlikely. Good judgement goes a long way.

ALWAYS take antibiotics till the end, side effects depend on what she is given. Some have mild nausea but some have significantly more serious side effects (stuff like vancomycin, rifampin, etc) BUT, your wife would not have gotten these. So, she should not have any real side effects.

Never take antibiotics if you don't need them.

If you started, you finish them to the end.

I don't think she's started and if they are useless in the first place you don't need to finish them.

They gave them to her to prevent infection.

When did this happen? He said the doctor just told her to get rest.

And don't antibiotics cure infections, not prevent?

They can prevent. That's called prophylactic. Sometimes they can be given to people (im assuming doctor gave them since he has some?) who have an injury that risks infection, or have a condition (ex heart murmur patients get use them before dental work) or have been exposed to an agent.