I honestly couldnt care less if they took more or less time than a station. If ship building times are fast enough that you need to worry about nerfing them for ships, then they need to be nerf for stations as well.
The problem isnt the spawning of ships in battle, since I sorta expect some crew update to fix that by requiring some NPCs for optimal performance. The problem comes in how do you destroy it, and what is the value of stations.
Factories and shipyards are key infrastructure to a faction, so in times of war you need to find and destroy the enemy's ability to produce things. Being able to find these ships, and them not just insta-jumping away 20 seconds in is the key to this problem. Maybe buff inhibitors against it? Disabling jumpdrives is kinda extreme in hindsight, since travel is very slow without it, but there needs to be ways to counter that to some degree (not a full counter, but just enough to keep it balanced).
There is also the issue of stations. Maybe make salvage fleets/commands only work within a certain range of a station? Maybe give stations the ability to give AoE buffs to allies? Something more than just invincibility (which is honestly something many of us are getting tired of to some degree), and the 3 block station needed to claim a system.
Those are just what I would focus on thinking about. Would love to have small shipyards and factories on ships, but in the current state of the game, I'd have to say no.