If there is a time limit, I prefer one long enough that your character should be dead by old age when it happens; somewhere between fifty to hundred years.
I'm still not sure I like the 25-ship limit idea; I feel like there are more organic ways to make fleets above X size unattractive that aren't so much of an obvious fiat, but I'm sure Alex had a good reason for that change and I rarely ever have played with a fleet bigger than that, outside of Vacuum, so it's somewhat moot
I have done this frequently in the endgame due to frigates being the best ship class to use due to a combination of high burn speed from Navigation 10, cheap to maintain due to supply efficiency, and fast CR recovery times. When not hauling commodities, my fleet has nothing but frigates - more than forty of them!
Admittedly, 25 ship limit will stop them, and with Navigation bonuses reversed, bigger ships look more attractive. I might end up going for a mostly destroyer and/or cruiser fleet, with a few frigates for special tasks (e.g., Hyperion for space superiority, shuttles or Hound for boarding).
On the other hand, at least Logistics is gone, and I do not need to invest in Leadership/Fleet Logistics to run a big fleet. Given how much fun Combat and Technology are, I do not have the Logistics to use more than a few small ships until about level 50+, when I transition from chain-flagships to a fleet rush. (This is one reason why I consider endgame to be when the game truly begins; levels 1-50 feel like tutorial mode/grind-fest for me.)
I will not like the 25 ship limit if the AI can use more ships. This easily falls into 'AI is a cheater' trope.