@Watermelons - You raise a good point! For medical reasons, my rabbit was seeing a vet weekly during that time period, and so he was regularly being "felt" for them as well (so a neuter could be scheduled). It is absolutely possible that it may have been sooner though.
@Preitler - do they suck them in due to heat? I knew they do it, but never thought about why. I realized my rabbit's had dropped because when I was carrying him, I felt something unfamiliar down there, brushing up against my hand (my hand was supporting his bottom). I thought maybe they do it for mobility purposes, because when they dropped, my rabbit started hopping somewhat unusually, like he wasn't sure what to do with the extra momentum, haha.
No, normally they drop it when it's hot, testicles need to be cooler than body temperature. Not much difference to us humans, only we can't pull them completly in when it's cold or something we do not like is messing with them.