Roughly about 7 or 8 months ago, I had to leave my guinea pigs in the care of a wonderful lady who runs one of the rescues this forum has only good words for

I rang up once a week to check up on them and how they were doing, and they were there for about two months before my circumstances dictated that I couldn't bring them home again, and she'd be rehoming them for me.
I made the call one day, after they'd been there several weeks already, and she put me on speakerphone and placed the phone in or near their cage, I'm not sure which. As soon as they heard my voice, they were apparently looking around to see where I was. They won't forget. You've got several months to work on that bond with them, but they won't forget their humans.