Hi jcat_3,
Unfortunately there is no way to answer this specifically because it can very greatly from person to person. Some people can certainly feel some pain or discomfort during the break in and adjustment period while some people sleep well on their mattress right from the first day. Of course “symptoms” of pain and discomfort that don’t start getting better after a few weeks or that get worse can be the result of choosing a mattress that isn’t a suitable “match” for you in terms of “comfort”, firmness, and PPP in which case you would need to either return the mattress or make other “adjustments” such as adding a mattress pad or a topper.
In general though … there will be a break in and adjustment period for any new mattress or sleeping system as the mattress loses any of it’s “false firmness” and the cover stretches and loosens a little and the materials settle and your body gets used to a sleeping surface that is different from what it is used to (see post #3 here and post #2 here). This would typically be a few weeks but it can be shorter or longer depending on the specifics of the person and the mattress (higher density materials can take longer) and it can be surprising to many people how much their sleeping experience can change over the course of the first month or so. I would generally suggest sleeping on any new mattress for a few weeks at a minimum (preferably a month or so) whenever possible before deciding on whether it’s a good “match” in terms of comfort, firmness, and PPP and/or deciding to make any changes or additions to your mattress.
While it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because they can be very complex and there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress in terms of “comfort”, firmness, and PPP or any “symptoms” they experience … there is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here that may be helpful.
Phoenix