When you enter date in search conditions RT uses powerful module Time::ParseDate that allows you to use relative date/time formats.
- created more than 3 days ago Created < "-3 days"
- due date between now and 2 days from now Due > "now" AND Due < "+2 days"
- created last Sunday
Created = "last Sunday"
- created last Saturday
Created = "last Saturday"
The 'last <day name>' format can be used for any day of the week
See module description for other formats.