You can adjust a site's conversion window length in your "Site Settings" panel in your dashboard.
A "Conversion Lookback Window" indicates how long your campaigns will count conversions for after a view or click occurs.
With a 7-day post-click Conversion Lookback Window, for example, if someone clicks an ad and converts 7 days later, that will be counted as a conversion. If someone clicks and converts 8 days later, it will not.
Post-view conversions are conversions after someone loads an ad on a web site. Post-click conversions are after someone clicks an ad.