Here’s a super quick, completely un-edited video of working on sit-stay with my cat, Scuzzy. Scuzzy has a pretty good sit, but I’ve never asked for duration or eye contact.
In the first 1:25ish, I’m marking and rewarding when Scuzzy offers sustained eye contact. If your puppy isn’t capable of sitting long enough to offer eye contact, you may want to work on that in a down-stay or doing doggy zen first to make sit-stay easier on them. It’s generally easier for dogs with better eye contact to maintain stay positions, because they’re able to focus on you instead of being distracted by the environment.
In the last part of the video, I’m rewarding Scuzzy rapidly for staying in position, and I introduce a release word. When Scuzzy broke position, I chose to wait for him to offer it again because he has a strong sit behaviour. If your puppy isn’t very good at offering sits, give them their release cue (I’m using “break” in the video), ignore them for a few seconds (keep them on leash if they’ll get into trouble when you ignore them), and reposition them. Your puppy should learn pretty quickly that staying in position brings lots of food, but moving around is boring. Over time, you can gradually increase the amount of time between treats until you’re only rewarding every few minutes. Once you’ve introduced a bit of a break between rewards, you can start selectively rewarding for eye contact to help build your puppy’s focus like in the previous method.