You can do this by adding a qualifier with the following format to your search query:

[-]created:<comparison operator>@today[+|-<duration quantity><duration unit>]

where the components are:

• - (optional): exclusion operator
• created:: creation date qualifier
• <comparison operator>: one of the operators listed here
• @today: expands to today's date
• +|-<duration quantity><duration unit> (optional): deviation from current date
  • + / -: direction of deviation
  • <duration quantity>: a number
  • <duration unit>: identifier for the unit of duration:
    • d: days
    • w: weeks
    • m: months
    • y: years

So if you want to get issues created less than 7 days ago, you would add this qualifier to your search query:

created:>@today-7d

Unfortunately this feature is not mentioned in the relevant documentation, so this related documentation for GitHub Projects is the closest thing to an authoritative reference:

https://docs.github.com/issues/planning-and-tracking-with-projects/customizing-views-in-your-project/filtering-projects#filtering-for-when-an-item-was-last-updated