The Overdrive books don't expire but the One Click Digital files do. Just posting as some libraries offer both services.
BTW, I hadn't noticed the 14 day check-out limit on FLP, just that they'd starting limiting checkouts to 6. That's not a problem for audio books but e books are another story
for slower readers (like me). Luckily my local library is doubling their digital content budget this year so I'll be saving myself the $35 FLP fee when my card's up for renewal.