Time isn't exactly linear nowadays. It's constantly getting pauses, resumed, sent back to a previous time, and sometimes even forward.
These are neither constant nor common. I can't recall a time when it's been paused, sent back to a previous time or sent into the future. I'm not sure how it's even possible for time to do that. People, yes, like Pelinal's armour and probably Pelinal himself reputedly being from a future time. Pauses wouldn't really make sense, since we notice time by its motion. Dragonbreaks ae the nonlinearity of time, which is a different thing entirely.
You just contradicted yourself when you wrote: "time in Nirn is linear" in the first sentence and then writing in the second sentence: "whereas time in Nirn is not linear", unless that was a typo.
He meant "where" not "whereas". "dragonbreaks, where time is not linear."