And when does it end?
Edit: I should ask, when does a winning core get established.
It ends when the young players they've acquired start making something of themselves. I think what we hope is that Keller continues to be Keller and in a couple more years Cooley and Guenther are knocking on the door to stardom and pushing Keller for best player on the team. At that point Simashev and But should be in their 2nd season in the NHL and showing the same flashes Cooley and Guenther are showing now. Geekie, Doan, and Lamoreaux in there as well. At that point hopefully the other high picks they will draft this summer are knocking on the NHL too. The year after that, the picks from 2025. That's basically what a pipeline is, it's a stready flow of talent and you have to have it because you never know which picks are going to succeed and which ones are going to disappoint.
As BA states you have to stack good player on top of good player and you do that continuosly until the players elevate the team to playoffs and hopefully contender. Until that happens, you keep plugging along. It's going to take a long time because they had almost zero pipline thanks to Barroway/Chayka. It's one thing to inherit a bad team, it's quite another to inherit bad team that has empty cupboards. It's frustrating but no one should be surprised where the team is at right now. It's going to take time, I'd say at a minimum 2 more years before they're a legit bubble team and even that depends heavily on Cooley and Guenther being the real deal.
My realistic prediction (IF and ONLY IF they stay the current course):
26-27 - bubble team
28-29 - squeek into playoffs
29-30 - expected to do some damage in playoffs but is not a contender
30-31 - darkhorse pick for contender
31-32 - contender