1st solution :
I don't know if it is the best way, but you could store the date of the creation of the new node in a database.
Then, when you refresh your TreeView, use something like this :
For Each node In TreeView.Nodes
' remove 5 days from today's date
' --> make sure that you use the good date format
If field >= today.AddDays(-5) then
TreeView.Nodes(i).ForeColor = Color.Red
2nd solution :
Maybe you could create new tree nodes depending on the current date.
When you add a new node, make sure you change it's name and not it's text property. Then you can create an array with all your nodes and loop through with the following condition :
If nodeName.Substring(nodeName.Length - 10) >= CStr(Date.Today.AddDays(-5)) Then ...