thats happening because you are asking to evaluate whatever is in self ≥ "this string".
String evaluation compares the ascii values of "this string" to whatever is in Self.
If Self has Time value (hh:mm:ss) then...
hour(self)≥8 should do the trick.
if Self has a text value then you will have to figure out how to extract the hour value from the text
if Self is an number(integer of total hours) then Self≥8 will work