How long to let 3-5" rounds dry?

Longer than you would imagine. I cleared about 6-8 cords worth of wood from my property 2 years ago. 60% maple, 25% black cherry, 15% oak. I saved all the limbs larger than my wrist to be cut into 16" sections.

One year later (last year) the wood that had been split was burnable at lower 20%'s for moisture. Not ideal but I needed to burn it. Strangely, every time I burnt a section of limb it sizzled, hissed, and bubbled. This year (two years later) the wood that has been split is mid-high teens for moisture and the limbs are around 20%.

So I would say that the limbs take one year longer than wood that has been split. I would have expected the opposite, but thats not what I found in my case.

Yep, the rounds and larger limbs def take longer. I have 1 yr old cherry rounds of about 4 or 5" that are still too wet. The splits are about ready though.

I use my arm as a gauge, anything bigger gets split. I'm finding it makes it easier to get more wood in the fire box that way. Splits stack a little tighter than rounds. And tend to start off gassing sooner as well from what I've noticed.

That's the gotcha with small rounds. They're covered in bark and bark holds in moisture. I've tried to burn 2-year-old oak limb cuttings, 3" diameter... no soap. They just wouldn't cure completely in the round.

It's extra work and time to halve little rounds, true but they will cure much faster. Anything 3" and larger gets busted here. Besides, it makes great starter wood.

You gotta tell us what species.\
Regular sized splits single-stacked off the ground in an exposed spot can take anywhere from half a year to over 2 years depending on species and time of year it was stacked (it'll dry way quicker in summer than winter).
Generally the small, un-split rounds take longer to season in my experience, but some dispute that. I try to separate them from the splits for 2 reasons: take longer to season and I like them for overnight burns.
So, if we say your splits will be good to go in a year, the small rounds my take 18 months. If this is Oak, make that 2 years min for splits & maybe 3 for small rounds.

Whatever you think....Times 2!

I have quite a pile of red oak limbs, roughly the same size as you mentioned. They should be ready to burn in 2025-26.

I'd give them 4 to 5 years in the open with wind and sun, covered.

I'm not sure I have ever had seasoned small rounds. I usually throw them in on top of a good roaring fire.
Two years sitting and they hiss with foam pouring out of the ends.