Haven’t tested myself, but my understanding is the following:
IPNS will be propagated from peer to peer as soon as they are emited. Each peer will only keep the newest record and ignore the older ones (each IPNS has a timestamp) even if they receive them after the newest. Each peer will serve the newest record they know about, timestamp-wise.
When you request the latest IPNS record, you will ask several peers. IIRC IPFS will accept a record if 3 different peers say a particular record is the last one. I don’t know if it checks a signature from the IPNS key (I think not yet implemented, but it will in the future). I don’t know if it checks against the timestamp yet either.
So, i don’t know if you will end up with an outdated record (if you don’t check the date), or fail to fetch (because you always hear about a newer record, but never reach the threshold of 3).
To avoid problems, the time between updates should be much larger than the time it takes for records to propagate in the network (just like blockchain). I don’t know where the practical limit is as of now.
I think a better solution for frequently updated data would be to have a stable IPNS record pointing to DB like orbit-db or similar.