How does it work exactly? I know in an auction of course how it works, but if you just have a selling thread up and it says

For Example:
*Item being sold here*
HB: $30
AB: $90

How do you decide when you take the HB or if you will? Do you give it a week, a few days? I know it might sound like a silly question but I just want to make sure I know how these things work >>