In our case what happens is that the "release day" is not a fixed day because there was too much to test and this is a problem that speaks for itself :D
I'll work on changing the approach!
We struggled too, as our tester was part of another department, hardly ever available. Once we managed to explain management it's a bottle neck, and it didn't happen over night, eventually we got dedicated tester for our team. Think it was around two years ago. It has made a massive difference, we get our feedback very quickly, no slipping deadlines, everyone's happy :)
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