Some years back, I got real scientific and measured the hardness of cast bullets of various alloys at one week intervals to see how much they hardened and how long it took.

I found they did age harden, some only took 2 weeks to max out, others 3 weeks and one took 4 weeks, depending on the alloy. After that some alloys lost a little from their new hardness, but some did not and were very stable. The really big thing I learned is they didn't hardened enough to make any difference in my loading. A Bhn point or two one way or another is irrelevant for practical shooting. Like some other things that folks get fixated on, this is a non-issue.

I cast and put them away and size as needed. Hardness has nothing to do with this. It is just easier and who knows what size I will want them when the time comes to load. So, just do whatever you want to do, it will make no difference in anything other than irrelevant theory.