I would call and talk to Buds.

Select 90-day layaway when you checkout. After checkout is complete go back in and pay a minimum of 20% down on the layaway. That will secure the firearm at the price desired. Then when you get back you can pay off the remainder immediately or pay it off over the 90-day period as you desire.

Layaway is great and when you're checking out, you should see a place to pick layaway. I just did this and it worked perfectly! It was great, seamless and very convenient!
Just a note, when I did layaway, I paid with a gift card for my down payment so when I went to make another payment, it defaulted to me mailing in checks or money orders. I had to contact them via chat and they updated it to credit card (2 minute process but I think this was because I used a gift card to start the purchase). It's way easier than trying to delay shipment for such a large store.

You'll definitely want to talk directly to Buds about that. However, I was in a similar situation and spoke with my FFL, they were kind enough to hold the firearm for a few weeks before I could make it home. That may be a second option for you if the shipping cannot be delayed. Hope that helps!