@Anelisse Hi Anelisse! I’ve done quite a bit of research, since we thought my husband might only be able to fully join me between 6 months and a year later. It’s definitely a grey area, but from what I’ve found, they generally understand that the first year can take time to fully relocate, sell your house, etc. Popping by occasionally while you’re in the process of moving seems fine in that first year. It’s not the same as someone who is already established and leaves for over a year and never returns to the U.S. (that’s when you’d need the I-131 re-entry permit).
From what I’ve gathered, you just need to activate your green card within the 6 months, then make sure you’re spending some time in the U.S., even short visits, and building ties here (like opening a bank account, getting a driver’s license, etc.). The “6 months to 1 year” concern usually applies if you don’t come at all. Since we’re coming from Canada, it’s relatively easy to at least visit and build ties even if you didn't totally move yet.
Feel free to DM me if you’d like to chat more about it!