Temperature and humidity changes should be avoided. Use a ziplock.

I store tomato seeds in coin envelopes in my office - get excellent germination up to about 14 years - things drop off drastically at age 16.

Peppers and eggplants have much shorter duration - 5 or 6 years then big drop off.

Each flower type will have a different duration.

Freezing will definitely prolong life - but keep the moisture out - and let them come to room temp before opening whatever container you use so that moisture doesn't rush in.