If they say in a week that should mean Monday... but it really depends on the place. I had one place tell me they would let me know by the end of the week but didn't hear from them so I took another position and then they called me maybe a week or so later saying they wanted me. If you don't hear from them, just call... worst case scenario they say "Oh yeah, we chose someone else" but some people appreciate when you make the effort to contact them.