How long does the neck relief on a new guitar take to settle down once you get it home

ToneControl

I bought a new PRS SE this week
action is a little high. but neck relief is more than normal. How long should I wait before tweaking the truss rod?

BillDL

Tighten the truss rod now to reduce the relief to a good average, set your action to a good height, and then monitor it for changes in the different environment over the next few weeks and adjust the truss rod as needed.  After you have set your action on a guitar with a good relief the only thing that's then likely to change will be the relief.

Roland

I give it 48hours. However it can move over several weeks. If the frets are going to sprout then that could be longer. 

ToneControl

I'm assuming the humidity was low in the warehouse. I manage the humidity in my guitar room to around 50%
I'm also assuming that cardboard plus soft case would allow the low humidity to reach the guitar during storage

ICBM

Adjust it as soon as it needs it.

I thought you meant a slightly different question - how long may you have to *keep* adjusting it for until the neck stabilises completely... the answer to that can be up to a couple of years. (Maybe more, but I don't have personal experience of that.)