Would am opened packet of 05 in a ziplock be less fresh than one sealed in the packet? If so, any thoughts on how long it’ll last?
Yes, it would be less fresh. FWIW, the 2 times I saved an open pack of dry yeast and reused it, I had bad results. Good luck to you!
There is always a fear that contamination may occur. Consider using it in your next boil as a yeast nutrient…I am advised that yeast hulls help the active yeast health. That is purely anecdotal, so YMMV, of course.
us-o5 makes tasty pizza dough as well. slow to rise though