They can't take too long, that would be a failure by tself to take 4 years to see that the design is working.
Or you can have not working ships you paid a billion each. Surely timeframe will shorten once the first ship takes shape and others will take less time to incur into service.
But the idea that we are just building ships at a breakneck speed and this is just a slow down of what's usually expected is wrong. We are building many ships because we have many shipyards. We are not particularly building them fast. Follow on Istifs are taking 3+ years from ordering to incurring. 5 years for a destroyer is normal. A single Tepe has "more radars" than what, 5 Istifs combined?
Since Goeben itself, we never operated a ship of this caliber contemporarily. It's new to us. Our most potent active use AA missile is still SM-1MR. We are going to handle theater air defence and ABM with Tepe Class. There are many mistakes to make and then correct; there's a whole EW suite that is to be built and a radar suite to be confirmed in real world. Single Tepe carries 96 VLS, that's 12 MIDLAS 8-cell VLS. We didn't yet build and deliver 12 MIDLAS.
To be honest looking at all this, it just makes sense some sense to get a foreign design if we can build and incur it in 3 years as a stopgap.