First of all, let me ask you a question: according to which Code (or Standard) are you making that weld?
One hour soak seems to be too long a time for 5 mm thickness. I'm accostumed to shorter times for 5 mm thicknesses.
This means that the conditions you mention SHOULD be OK. I've deliberately underlined SHOULD because, as a matter of fact, unless someone has the crystal ball, nobody knows what exactly the hardness will be after the PWHT. It depends, among other parameters, on what was the hardness BEFORE the treatment.
You shouldn't bother, though. When the first PWHT doesn't result in the required hardness, as sometimes happens to everybody, it is repeated again.
Giovanni S. Crisi
Sao Paulo - Brazil