You might of seen my post, but if not here is the approximate grind time in all its glory.
roughly 800k is roughly 100 hours (I'll have to actually test my income over a couple hours tomorrow if no one beats me to it). 100 hours for 1 t5 ship with mods you want, if you want officer briefings then you need 3 more t4 ships. So let's say 250k for each t4 to get the ship and mods.
Totally optimized using straight line tiers and fleet payments and rotating through the ships you're using with a focus on the one going for t5 resulting in your t5 maxing and t4s hitting officer briefs all at the same time..... roughly 127 hours. Another 153 to get the remaining 3 t4s to t5 loaded. But on the bright side if you go for all 4 at the same time straight to t5 it's only a paltry total of ..... drum roll please....
..... 262 Hours!
Getting a t3 fleet doesn't take very long but as Ananym said, its pretty useless since you'll get stomped by any decent player in t4. Also the t4 and t5 ships and mods increase in price by a ridiculous amount with basically no increase in income.
This is a pretty rough approximation so if anyone has more accurate numbers or even just slightly better math skills feel free to update it.
Why bother unlocking T5 though? Just longer queue times and higher maintenance cost, all with less chances of winning a match. Just unlocking 4 T4 ships and playing in veteran bracket with them against T2 players who don't know how to exclude their recruit fleet from the veteran MM should be counted as finishing the game imo.