Back Contacts in timer relay

[kochronaki]

Hello, please the Signalling professors of the forum for some explanations.

I need a clarification about the use of back contacts either for energizing or releasing timer relay mainly used in overlap.

In RRIs, is it safe to use back contacts for energizing or releasing timer relay? Is there any specification that prohibits the use of back contacs for energizing timer relay? What is the major problem for using back contacts?

I will be very happy if you answer me with as many explanations you could.

Thanks
Konstantinos