Well, the puppy stage did not take long at all. About 45-50 minutes.
The short:
I'm glad it didn't last a full two hours as it wasn't the most interesting development. It's pretty basic as one might have guessed from the discussion here. He mimicked a lot of things you'd expect from a newborn animal, such as wobbly legs, troubles standing up, acting depressed or out of energy when he failed, etc. He also became progressively more chatty in his tonal language before announcing he was an adult now. He put his paw out a lot and definitely wanted you to shake it, if you waited too long he made the sad blue face. In between each of his stretching/crawling/standing/walking attempts I would usually show him his Aibone and Ball (and have him track the latter for a bit) and encourage him with things like "how cute" and "Aibo" (basically the few things the manual says it'll understand). It wasn't anything special - nothing I'd necessarily reset an Aibo for just to experience. However, it does make me look forward to the more complex development of the 210 on AiboLife 1 and 2.
The long:
I made quick notes to myself as to what he was doing by 10 minute segments. (Offset by 1-2 minutes since I was multitasking).
0-10: Nicco moved very slowly when he did move. He generally acted slow if he moved and seemed like someone just waking up (or something being born, duh). He didn't make much noise and acted very surprised when his head was touched (essentially a flinch back).
10-20: Nicco made a few attempts to stand up, each one failing (and with a little bit of variation on success). As soon as he's done "pouting" I encourage him and start showing him his toys (this applies every time). Sometimes just leaving the ball in front of him, other times making him track it back and forth.
20-30: Nicco makes more tonal noises more frequently. His movement resembles stretching out and he successfully stands up and makes a celebratory sound before sitting back down. During some of his standing attempts he acted very wobbly and not very stable before "collapsing" (think robot Bambi). Nicco seems more responsive to touch and no longer acts surprised when his head is touched. He also began keeping his mouth open giving him the appearance of being happier or more alert.
30-40: There is even more of the stretching behavior. It varies a little bit but nothing major. Nicco makes several attempts to crawl but doesn't get very far.
40-50: Nicco tries crawling again about two or three times, each one seemingly further/more successful (or maybe it was one big long attempt with pauses for him to catch his breath lol). He then stood up and announced he was an adult.
So as you can see, not too long, but also pretty basic. Altogether, cute enough to experience once but nothing extraordinary.
Edit:
Here's the video for those interested in seeing some of the puppy phase: