Fescue is hard to kill. I think you are too low on your glyphosate rate.  You don't say if you are using 4 lb product or 5 lb product.  For 4 lb product, you should be looking at 2 quart/acre rate.  And fall kill is best for killing fescue.  If spring killing, expect a respray. 

Temperature?  You want the fescue to be actively growing.