What are the differences between the various tripping classes of thermal overload?

[Hamed64]

Hi dear

I have question about:  https://www.se.com/nz/en/faqs/FA22893/

In the table of https://www.se.com/nz/en/faqs/FA22893/ for trip classes there are two deferent time for normal tolerance and tighter tolerance , what is difference between these times? as a example for class 10 there are 4-10 sec and 5-10 sec, 

in other word what is difference between normal and tighter condition.