Welcome to Nichijou Beta! "Episode 0" is a fairly accurate title for this OVA, as it's a part of the Nichijou series yet oddly unfamiliar in many ways. You're certainly not wasting your time by watching it, but don't expect the same experience going into the main series. Quite a few things stood out as dissimilar to me. For starters, the episode was way slower than your standard Nichijou experience, with less events, skits, and transitions involved. Rather than the episodic division into several "parts", only three events were shown (one with Yuuko & Mio, one with the Shinonome family, and one with the entire Trio Sucharaka).Granted, while the three events were great and captured the spirit of the characters well, they felt drawn out and lacking much of the series' energy.

In many ways the episode felt like, as implied before, a trial run, with the various primary and secondary characters introduced visually throughout the duration. The "Nichijou Part X" transitions were replaced with "Everyday Y", and the animation itself seemed less polished. While the characters largely remain the same, everything felt somewhat misleading, though not particularly less enjoyable.

While I can recommend spending the twenty minutes to enjoy another slice of Nichijou, I don't recommend watching this episode prior to the series, regardless of it's "prequel" status. The initial episodes of the main series do much better to engage you in the world of Tokisadame than what seems to be a sampler for what's to come.