Unbound has "prefetch" which will refresh near-expired cached records, and various other cache/ttl knobs. "serve-expired" seemed to work well too

I use both of those as well in Unbound.

I was thinking that if you preload your 50k list and override the min-ttl, the prefetch would let you relax the cron schedule a little

	▲	Bender an hour ago \| parent [-]
		I could but I like to run everything in cron hourly to force trigger the retry mechanisms on the expired records and make a bunch of noise so that my network always looks active. It's just a "me" thing. Others can and should do whatever they think will work for them. If everyone does this a little different that is probably best.