What’s the issue with the “for just minutes” line?? I think it’s pretty straightforward:
The original plan is to disable the tower on the ground, when they reach Exegol Pride switches the signal to the command ship, so the plan changes to disable the tower on the ship, they succeed in disabling it, which leaves the ships stuck “for just minutes” (Poe reiterates this by saying “Nav signal’s down, but not for long!”), but Finn decides to take the whole ship down, which leaves the fleet stuck for good.
Of course there’s still the tower on the ground someone could fire back up, but at that point there’s a whole galaxy of ships attacking the Sith Fleet on their bright red weak point so it’s safe to say “they’re toast”. The whole fleet is destoryed, and the people who built it are crushed by rocks, so it’s all taken care of. The whole thing is kinda dumb, but if we removed all the dumb things in this movie we’d be left with nothing. In this case removing the line would turn the plan into a “we do this one thing and we win, period.” wich would massively lower the stakes of the Exegol assault. Instead the plan is to stall the ships from leaving Exegol long enough for Lando to rile up ‘the galaxy’ to come and take them down.
Disabling the navigation systems is not the main goal or the win condition, the plan was always to temporairly delay the Final Order. In fact their “victory” in disabling the tower happens during the ‘lowest point’ in the battle, since “no one is coming to help them”.