How long does it usually take to hear back from an interview?

So I had an interview as a cafe assistant about 8 days ago and haven't heard back. At the interview we (group interview) were told we'd find out the outcome within a week, should I wait a few more days or follow up with them? Not sure if because it's a cafe they might be busier than usual at this time due to them putting out a range of valentine's products and therefore maybe they just haven't gotten round to it.

In terms of following up with them, should I do this by phone or is email fine? Where I live, the phone reception is spotty so often it's hard to hear each other and my phone manner is no where near as good as my in person manner. Hence why I would prefer email but is email a bad way to follow up?

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official